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GEO Assessment - GEO Geological Review - 1/18/2008
Y ■ �'��., �,xc p v O �w cv�e r KENNETH NEAL & ASSOCIATES' 2 CONSULTING ENGINEERING GEOLOGISTS - 3314 Gibraltar Ct. S.E.,Olympia,WA 98501- 96$ `a`� Telephone: (360)352-5125 Fax: (360)236-020I--'-- Wa la e-mail: kengnea aoLcom 0- January 18,2008 MEMORANDUM TO: Mason County Department of Community Development ATTENTION: Robert D.Fink,AICP,Planning Manager Engineering Geologist 100 FROM: Kenneth G.Neal,L.G.,L.E.G.,Principal Engineering Geologist KENNETH G. NEAI SUBJECT: Review Comments—BLD 2007-01647 _ "Ricker Residential Property Geotechnical Report, Tax Parcel No. _ 121187590020,Grapeview,Washington," report by Jerome W. Morrissette & Associates Inc.,P.S.,dated 14 January 2008. In my judgment, the report listed above meets the minimum criteria for a "geotechnical report" as outlined in the Mason County Resource Ordinance. There are two comments in the report that warrant careful consideration: I disagree with one comment in the report, on Page 20, which recommends the removal of large woody vegetation along the top of the bluff and five feet back from the bluff face. Research by the USDA Forest Service has shown that the benefits of live root structures far outweigh the risk imposed by loads placed on a slope by trees. This is demonstrated by the cover picture of the report, which shows root structures supporting the overhang along the top of the bluff. Trees should only be removed along a marine bluff if the type of tree is conducive to regeneration of growth from the root structure following cutting, or if the tree poses a threat to safety. The comment on Page 20, stating that, "It is possible in the future that a bluff toe bulkhead may be warranted to extend the economic life of the project site" suggests that the rate of bluff retreat may place the building site in jeopardy over the life of the residential structure. New bulkheads should not be a consideration, not even a future consideration, to extend the life of residences located with setbacks established under the current Mason County Resource Ordinance. If you have any questions,I can most easily be reached at my cell phone, 360-280-6180. 2 copies submitted KENNETH NEAL & ASSOCIATES CONSULTING ENGINEERING GEOLOGISTS 3314 Gibraltar Ct. S.E.,Olympia,WA 98501-3968 —,—� Telephone: (360)352-5125 Fax: (360)236-0201 �° Wash��f e-mail: kengneal@aoLcom rij o� October 8,2007 MEMORANDUM TO: Mason County Department of Community Development Engineering cecl c ATTENTION: Robert D.Fink,AICP,Planning Manager %enS�00 FROM: Kenneth G.Neal,L.G.,L.E.G.,Principal Engineering Geologist KENNETH G. NEAP SUBJECT: Review Comments—BLD 2007-01647 "Ricker Residential Property Geological Assessment, Tax Parcel No. 121187590020,Grapeview,Washington," report by Jerome W. Morrissette & Associates Inc.,P.S.,dated 12 June 2006. Since the building site is situated within 300 feet of a slope( marine bluff)over 10 feet high and inclined at over 40 percent, it meets the criteria outlined in Mason County Resource Ordinance (MCRO) 17.01.100E1, Category a, which requires that a geotechnical report be prepared. MCRO 17.01.100E2 Waiver of Geotechnical Report authorizes the director to waive the requirements for the geotechnical report for Category c and d sites, but not for Category a. For that reason, a geotechnical report will be required for this site. It should also be noted that the assessment was submitted to the owner over one year ago, which exceeds the unwritten six-month maximum policy from report date for submittal to the county. If you have any questions, I can most easily be reached at my cell phone, 360-280-6180. 2 copies submitted owyw i fi RICKER RESIDENTIAL PROPERTY GEOLOGICAL ASSESSMENT TAX PARCEL NO. 121187.590020 GRAPEVIEW, WASHINGTON or` r:'` •Ti.. L<a 1, -% t .�f '� .�. . . 1'+1�7-''i,!'?`;'f � •A .ram". � �'' .. ' PREPARED BY: EDWARD A. WILTSIE, PE 12 June 2006 1 Jerome W.Morrissette&Associates Inc., P.S. ' Civil•Municipal •Geotechnical Engineering and Planning 1700 Cooper Point Road SW,#B-2, Olympia,WA 98502-1110 (360)352-9456 / FAX(360)352-9990 _JWW Jerome W.Morrissette&Associates Inc., P.S. Civil•Municipal•Geotechnical Engineering and Planning 1700 Cooper Point Road SW,#13-2,Olympia,WA 98502-1110 (360)352-9456 / FAX(360)352-9990 RICKER RESIDENTIAL PROPERTY GEOLOGICAL ASSESSMENT GRAPEVIEW,WASHINGTON 12 June 2006 INTRODUCTION The purpose of this report is to provide geotechnical site evaluation data in accordance with the Mason County Landslide Hazard Areas Ordinance, Section 17.01.100 E for the project site,which is located at the end of Miner Road in Grapeview, Washington. The property consists of Tax Parcel No. 121187590020 in Section 18,Township 21 Range 1 West(see Figure 1). The investigations and evaluations performed for this report include published regional topography, published soil and geologic investigations and crude site specific topographic measurement of the slopes in the vicinity of the subject parcel. Neither site specific soil investigations nor detailed topographic surveys have been performed for this site as the substrata have been observed to be competent and there is no evidence of shallow or deep rotational failure in the immediate vicinity of the project site. The proposed structure would be located on the upper terrace fronting a competent glacial till marine bluff of about 35 ft height. The data gathered and investigations performed have been used to prepare general development recommendations. EXISTING CONDITIONS The site was inspected on 03 May 2006. The site is located along the north shore of Pickering Passage, about 3500 ft south of Grapeview Road and 4000 ft west of the southerly most point of Stretch Island(see Figures 1 and 2). The subject parcel is presently undeveloped, although the parcel immediately to the east includes a single family residence. The site is located in a generally undeveloped area that supports ground cover consisting of a dense stand of young third growth alders and Douglas Fir with an understory of salal, sword fern and Oregon grape (see Figure 3 and Photo 1). COASTAL ZONE ATLAS The Washington State Coastal Zone Atlas(see Figure 4) shows the property to be located along a section of shoreline designated as Stable with no indications of recent or ancient landslides. Ricker Geological Assessment 1 JWMA N06126 6/14/06 REGIONAL TOPOGRAPHY Figure 5 shows the regional topographic conditions in the vicinity of the project site. This site is located along and inland of a bluff slope fronting the north shore of Pickering Passage. The bluff slope rises nearly vertically approximately 35 ft from the highwater beach. The upland portion of the property occupies a gently undulating portion of glacial terrace that slopes gradually to the west toward an unnamed seasonal creek, which has been identified as a Type 4 Stream. The upland topography has apparently been formed by ancient erosive forces and drainage along the adjacent creek. There was no evidence of surface water courses, seepage or springs along the bluff slope or upland parcel area. ONSITE WASTEWATER SYSTEM AND WATER WELL There are no water wells or onsite wastewater systems on the subject property. LOCAL BATHYMETRY The immediately adjacent segment of Pickering Passage is approximately 18 meters deep along the central channel (see Figure 6). LITTORAL ENVIRONMENT The prevailing winds at the site approach from the southwest(see Figure 1). The site shoreline is oriented from about west southwest to east northeast. As such, the prevailing winds are oriented almost along the shoreline (see Figure 1). The longest deepwater fetches for this site are about 3 miles along the directon of the prevailing winds (along Pickering Passage). There is also a nearly 3 mile fetch extending southeast across Case Inlet, which includes deeper water, but is not along a major wind rose direction. The site is impacted by diffracted waves traveling along Case Inlet that bend around Dougall Point and approach the shoreline fronting the property. Figure 7 shows the general alongshore drift direction along the project site. Beach conditions indicated that the littoral transport system along the site is aggressive (see Photos 2 and 3). As noted previously, the bluff face is nearly vertical in the vicinity of the project site. The bluff toe along the property is comprised of very competent glacial till that appears to be highly resistant to wave action and surficial erosion. The surficial beach aggregate consist primarily of cobbles and small boulders, confirming an aggressive littoral environment. GEOLOGIC SETTING The project site is located along the south facing margin of the Mason Lake Glacial Drift Terrace (see Figure 8). Geologic Mapping presented in Water Supply Bulletin No. 29 prepared by the USGS shows Ricker Geological Assessment 2 JWMA N06126 6/14/2006 the project site to consist of Qvt Till (Pleistocene) sediments, consisting of cobbles and coarse gravel in a matrix of fine sand, silt and clay. Generally, the till is a compact, unsorted mixture and extensively underlies drift plains in thicknesses of a few feet to more than 50 ft. The till is poorly pervious, but has sand and gravel streaks that may yield quantities of perched groundwater. The till serves as a confining aquaclude to artesian water at some localities near sea level. The above described sediments were deposited by the glacial ice of the Puget Lobe of the Vashon Glacier about 12000 to 15000 years before present. Visual inspection of the project site confirmed the existence of shallow glacial till (see Photos 2 and 3). The exposed bluff face shows the referenced glacial till with a thickness of 30 to 35 ft. The exposed till appears to be competent and highly over consolidated with a mildly weathered surface. Regional topographic mapping suggests that glaciation followed by surficial erosion is responsible for the shaping of the ground surface in the vicinity of this site. SURFICIAL SOILS Surficial soils in the project area are mapped as Kitsap silt loam, 5 -15% slopes (see Figure 9). Observed site conditions were consistent with the silty loam surficial soil designation. Generally, the site soils consist of a variable thickness of silty loam overlying competent glacial till. SITE DEVELOPMENT Figure 10 shows a schematic layout of the proposed dwelling and associated facilities on the property. The dwelling will be located approximately 50 ft inland of the top of bluff. This location is outside of the 1:1 slope intercept from the toe of the bluff face, which is considered reasonable for competent glacial till as exists beneath this site. The dwelling is also outside of the 40 ft setback established by Section 1805 of the 2004 International Building Code. CONCLUSIONS AND RECOMMENDATIONS Based on the foregoing, it is concluded that: 1. The project site is mapped as Stable on the Washington State Coastal Zone Atlas with no indications of recent or ancient slope failures 2. Site observations indicate no surficial soil erosion, slope face springs or seepage areas, or shallow or deep slope failures 3. There are no seasonal or year-round surface water courses within the site. There is a seasonal Type 4 stream located to the west of the property on the adjacent parcel 4. Both shallow and deep soil structures indicate relatively stable conditions and sediment types that are resistant to deep slope failure mechanisms 5. Bluff face soils consist of competent glacial till that appears to be reasonably resistant to the aggressive littoral environment that exists along this site Ricker Geological Assessment 3 JWMA N06126 6/14/2006 6. The proposed site and adjacent surrounding properties are subject to becoming unstable due to site development and human activity,but can be maintained in a condition that will support the proposed site development as shown on Figure 10, if site conditions are considered and addressed during development and future use of the property 7. Site characteristics and proposed residential development on the subject site are such that a Geotechnical Report will not be required. In an effort to maintain the stable environment on the project site, it is recommended that: 1. Bluff toe area be protected by collecting and anchoring large drift log as the opportunity presents itself,to reduce bluff toe attack by local littoral forces 2. Remove large woody vegetation along top of bluff and 5 ft back from bluff edge, specifically the overhanging Madrona. Retain root structure to help stabilize top of bluff 3. Collected runoff from the roof, driveway and all other impervious areas in a tight pipe system. It would preferred that an easement be obtained from the neighbor to the west and site runoff be piped to the existing seasonal stream. If the easement can not be secured, it recommended that a holding tank and infiltration/disperson gallery be constructed along the westerly property boundary. As a last resort,runoff could be routed over the bluff to the adjacent beach via tight pipe to an energy absorption environment constructed on the beach 4. No surface runoff from the project site should be allowed to flow directly onto adjacent properties or over the bluff 5. Temporary perimeter silt fence should be installed to prevent sediment laden water from leaving the project site during construction 6. Disturbed site surfaces should be protected from erosion during construction through the use of plastic sheeting and/or chopped hay mulch 7. Surfaces that will remain disturbed for more than 14 days without permanent treatment should be seeded with annual rye grass and mulched with chopped hay 8. All existing and new disturbed site surfaces should be replanted as soon as possible with temporary erosion control grass seed and permanently with native plant groundcover 9. Landscaping should be designed to minimize the need for irrigation, as the introduction of additional water into the slope soils could be detrimental. It should be noted that water and gravity are the two most dangerous elements impacting a moderately to steeply sloped marine bluff sites. Extra care should be taken to maintain all potential water sources (domestic water pipelines, onsite wastewater pressure pipelines, etc.) and disturbed soil surfaces, along with appropriate site maintenance practices. Irrigation is not recommended on this site. Specifically, it is noted that all pressurized fluid transport pipelines be made of high density polyethylene plastic, i.e. drinking water supply and pumped wastewater to drainfield environment. Appendix A at the rear of this report presents details to aid in the construction of the site drainage system. Appendix B attached to the rear of this report provides background seismicity and geological information for Western Washington and the general formation of the Puget Sound margins. Ricker Geological Assessment 4 JWMA N06126 6/14/2006 Additionally, WSDOE has published three short manuals relating to site development and maintenance on marine bluff sites that provide a good reference source for maintaining the stability of your site. The WSDOE site can be reached via the internet at http://www.ecy.wa.gov/programsisea/shorelan.html. Look in the subsection titled Property Owner Guides. These manuals may also be obtained by calling the WSDOE publications center via(360)407-6000. Should you have any questions or require additional information, please contact me at(360)352-9456. Yours sincerely, J.W. Morrissette& Associates Inc.,P.S. Edward A. Wiltsie, P.E. Sr. Geotechnical Engineer/Associate A. 0c !L 1y 3 Ricker Geological Assessment 5 JWMA N06126 6/14/2006 FIGURES Ricker Geological Assessment 6 JWMA N06126 6/13/2006 D;_LJhi�l� ,� Vim -. ,`.Y r �• ,. �.VJ .. ^'• '1 1Y ��� • .• tea- � •.�..s � .�".r F Project A Site t } 1v L i 4k r ," Prevailing Winds R• •. E AND ASSICIATES INC., P.S. LOCATION CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 11-132 COOPER POINT '• D SW TAX PARCEL NO. 121187590020 �OLYMPIA,WASHINGTON1 WASHINGTON 61 .1)352�,.-' N06126 09 June 2006 Figure Topo USA®5.0 SHEL TlI Project Site ,R� r .. 29 wta - I Data use subject to license. O 2004 DeLorme.Topo USA®5 0. www.delorme.com 1 JWM&A JEROME W. MORRISSETTE AND ASSICIATES INC., P.S. ISOMETRIC VIEW LOOKING NORTH CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-132 COOPER POINT ROAD SW TAX PARCEL NO. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW, WASHINGTON (360)352-9456 FAX (360)352 N06126 09 June 2006 Figure 2 1 F Approx. 5 Project Site �+ a ' t M 4 � P S n x , N y R r C pi JWM&A JEROME W. MORRISSETTE AND ASSICIATES INC., P.S. OBLIQUE AERIAL PHOTOGRAPH CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-B2 COOPER POINT ROAD SW TAX PARCEL NO. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW, WASHINGTON TEL,(360)352-9456 FAX (360)352-9990 N06126 09 June 2006 Figure 3 `f v J u Scale 1:24,000 ? / 1 S I (� •INI IINN) IINI \�•IIl1 fi ; J U s '1 Protect Site � I J `\S " `U AU JWM&A JEROME W.MORRISSETTE AND ASSICIATES INC.,P.S. COASTAL ZONE ATLAS -SLOPE STABILITY CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-82 COOPER POINT ROAD SW TAX PARCEL N0. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW,WASHINGTON TEL.(360)352-9456 FAX (360)352-9990 N06126 09 June 2006 Figure 4 RCs Topo U '}S'4350 Fm= T.p.US 5.0 a Project Site 4 AL f � � �_ :.•-•_- r��'Y-�•�'r"1`7�,'.'.••,:%i'•• y -+ =- c�a'�"�.c <.'��+r���-•,r..+•i;'r I�,,;:s •�.?..'�'� j � -� ti'-� - _ _ - - }_~^�i'_�Y�=-.�'��_�_-�_ -y._ tie•�,,.Y;, ��`-- !" ti a Date use subject to license. C it O 2004 DeLorme.Topo USA®5.0. IYq n rm ym 0 2 use subject to license. MN(17.6'E) Data Zoom 15-0 0 � po 04 °��'To USA65.U. www.delorme.00m w AeWme.com JWM&A JEROME W. MORRISSETTE AND ASSICIATES INC., P.S. LOCAL TOPOGRAPHY CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-B2 COOPER POINT ROAD SW TAX PARCEL NO. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW,WASHINGTON no I'.no ')nnF Pirntra 5 I • C 160 • • Project Site • CJ j • _ 60 71 a Vo 2 /r 18 M • 1 � r 21 1 kb 14 0 18 'VrN0AA tool's JWM&A JEROME W. MORRISSETTE AND ASSICIATES INC., P.S. HAMMERSLEY INLET WATER DEPTH SOUNDINGS (meters) CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-82 COOPER POINT ROAD SW TAX PARCEL NO. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW, WASHINGTON TEL, (360)352-9456 FAX (360)352-9990 N06126 09 June 2006 Figure 6 s Lei YR" ,f` xz� A tub" I i = ► ✓ Drift Cells f Left to Right Right to Left ADivergence one ..... NAD Undefined r " + A'ap created by the INA State Cepartment of Ecology t+ JWM&A JEROME W. MORRISSETTE AND ASSICIATES INC., P.S. LITTORAL CELL MAP CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-62 COOPER POINT ROAD SW TAX PARCEL NO. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW, WASHINGTON TEL. (360)352-9456 FAX (360)352-9990 N06126 09 June 2006 Figure 7 �Ay1� 1 y t . Project Site Qvt Till,(Pleistocene) .1 i Cobbles and coarse gravel in matrix of fine sand, fir' I silt and clay. Generally,a compact, unsorted fi mixture. Extensively underlies drift plains in thicknesses of a few feet to more than 50 ft. �^ Poorly pervious, but has sand and gravel streaks taht may yield quantities of perched groundwater. Serves as confining aquaclude to artesian water i at some localities near sea level. ,l Taken from-Water Supply Bulletin No. 29- E Geology and Related Groundwater Occurance, Southeast Mason County,Washington, Molenaar f i 10, E r'• eat +��[l''i. I I I JWM&A JEROME W. MORRISSETTE AND ASSICIATES INC., P.S. GEOLOGIC MAP CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-B2 COOPER POINT ROAD SW TAX PARCEL NO. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW, WASHINGTON TEL. (360)352-9456 FAX (360)352-9990 N06126 09 June 2006 Figure 8 - North tlla�ui� LEGEND Kb - Kitsap silt loam, 5-15% slopes Kitsap silt loam-Occurs along the eastern edge of Mason County. Generally consists of r 6 to 8"of granular,friable, light brownish-gray i silt loam with high orgainic matter content. and many small hard to very hard shot: Project Site underlain by by a 16 to 20"thick layer of firm light brownish gray silt loam to silty clay loam with faint motteling and subangular blocky structure and less shot; underlain by light gray silty clay loam between 36 and 40 inches depth with faint motteling and weak subangular to weak platy structure and no shot. r Gravel till underlies the above soils at depths ranging from 3 to 10 ft or more. Taken from:Soil Survey-Mason County, Washington 1960 1 JWM&A JEROME W MORRISSETTE AND ASSICIATES INC., P.S. NRCS SURFICIAL SOIL MAP CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-132 COOPER POINT ROAD SW TAX PARCEL NO. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW, WASHINGTON TEL. (360)352-9456 FAX (360)352-9990 N06126 09 June 2006 Figure 9 I I � I . I j Driveway 4 Primary Drainfiel 1 � r Secondary I $ Drainfield x Ak �J 50, Proposed Dwelling Approx Top BALAVa of Slope --� � A � :� -• '`' � Tam I^, was•r�9� isa•s� tc 'ro SURVEYOR'S CERTIFICA TE IIS SURVEY CONFORMS TO THE MINIMUM JRVE'Y STANDARDS AS ESTABLISHED VOER ti!A.C_ JJ2-730-090 ;. Taken from Bechtolt 4 "' .... Survey Drawing JWM&A JEROME W.MORRISSETTE AND ASSICIATES INC.,P.S. SCHEMATIC SITE PLAN CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-132 COOPER POINT ROAD SW TAX PARCEL NO. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW, WASHINGTON (360)352-9456 FAX (360)352-91 N06126 09 June 2006 Figure 10 PHOTOGRAPHS Ricker Geological Assessment 7 JWMA N06126 6/13/2006 G N k d gy N 1Y .L y �W r L Y. i' a JWM&A JEROME W. MORRISSETTE AND ASSICIATES INC., P.S. UPLAND VEGETATION AND TOPOGRAPHY LOOKING SOUTH CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-62 COOPER POINT ROAD SW TAX PARCEL NO. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW, WASHINGTON TEL.(360)352-9456 FAX (360)352-9990 N06126 09 June 2006 Photo 1 gN G (y$aj F y 4 f •t '�ti. S�., ��t•'Y 4` Lc�i.. �.6w. lt.�'�... + 4 T. 4' ,r �V t y • r - I Y(G 9 ` JWM&A JEROME W. MORRISSETTE AND ASSICIATES INC., P.S. PAN OF BLUFF FACE LOOKING NORTH CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-62 COOPER POINT ROAD SW TAX PARCEL NO. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW, WASHINGTON TEL. (360)352-9456 FAX (360)352-9990 N06126 09 June 2006 Photo 2 t a f t 7' Pliffin JWM&A JEROME W. MORRISSETTE AND ASSICIATES INC., P.S. BLUFF TILL FACE AND BEACH SEDIMENT CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-B2 COOPER POINT ROAD SW TAX PARCEL NO. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW, WASHINGTON TEL.(360)352-9456 FAX (360)352-9990 N06126 09 June 2006 Photo 3 APPENDIX A DRAINAGE SYSTEM DETAILS Ricker Geological Assessment 8 JWMA N06126 6/13/2006 Roof Downspout Downspout to Cleanout PVC Transition Unit Ground Surface 4"PVC Cleanout Riser 4"PVC Wye Flow 4"Solid Wall PVC Roof Drain DETAIL ROOF DRAIN DOWN SPOUT/CLEANOUT (Not To Scale) OMIT JWM&A DETAILS JEROME W. MORRISSETTE &ASSOCIATES INC., P.S DOWNSPOUT/CLEANOUT& GRAVEL DRAIN CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-B2 COOPER POINT ROAD SW TAX PARCEL NO. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW, WASHINGTON TEL(360)352-9456 FAX(360)352-9990 rMM26 09 June 2OU6 F Igure 4" DIA. PVC 4" DIA. PVC THREADED CAP SOLID WALL PIPE 4" DIA. PVC THREADED MALE EXISTING ADAPTOR GROUND O O D�T 1 4" DIA. PVC °a 45' ELBOW o p -- 4" DIA. PERFORATED � a a PVC DRAIN PIPE LIMI T OF GRAVEL DRAIN DETAIL FOOTING DRAIN AND CLEANOUT N.T.S. JWM&A DETAILS JEROME W. MORRISSETTE &ASSOCIATES INC., P.S. FOOTING DRAIN CLEANOUT CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-B2 COOPER POINT ROAD SW TAX PARCEL NO. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW, WASHINGTON TEL(360)352-9456 FAX(360)352-9989 N06126 09 June 2006 Figure A3 FILTER FABRIC )A#kTERIAL Ei,' WIDE ROLLS �— USE STAPLES OR WIRE RING'S TO ATTACH FABRIC TO WIRE 2' x c x 14 Ga WIRE FABRIC OR EOUrVILENT t 0 ' I 719 1 i BURY BOTTOM OF FIL T ER MATERIAL 2'r IN $' x 1:f TFE41CH I 6' MAX Z x d' WOOD POSTS, STANDARD OR BETTER OR EQUAL ALTERNATE: STEEL FENCE POSTS NOT TO SCALE JWM&A DETAILS JEROME W. MORRISSETTE &ASSOCIATES INC., P.S. FILTER FABRIC SILT FENCE - FRONT VIEW CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-B2 COOPER POINT ROAD SW TAX PARCEL NO. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW, WASHINGTON TEL(360)352-9456 FAX(360)352-9989 N06126 09 June 2006 Figure A4 2" x Z" x 14 Glc WIRE: FABRIC OR EQUIV. FILTER FABRIC WokTER:AL S �� I f _ z lip- 0 ! -- �� 0 :. O I� i mal-�.r--I�. 1 PROVIDE =f 4' TO 1-1/2. � O ,.�I N WASHED ROCKCR DATIVE -s �0 �t� -- ! pACKFIU 04 BC.H SIDEZ. OF FILTER FABRIC FENCE ova i s i 2" x 4- WOOD eoST ALT. STEEL ;ENCE POSTS NOT TO SCALE JWM&A DETAILS JEROME W. MORRISSETTE &ASSOCIATES INC., P.S. FILTER FABRIC SILT FENCE -SIDE VIEW CIVIL AND MUNICIPAL ENGINEERING AND PLANNING RICKER RESIDENTIAL SITE GEOLOGICAL ASSESSMENT 1700-62 COOPER POINT ROAD SW TAX PARCEL NO. 121187590020 OLYMPIA,WASHINGTON 98502 GRAPEVIEW, WASHINGTON TEL(360)352-9456 FAX(360)352-9989 N06126 09 June 2006 Figure A5 APPENDIX B SEISMIC AND GEOLOGICAL BACKGROUND INFORMATION Ricker Geological Assessment 9 J WMA N06126 6/13/2006 SLOPE STABILITY AND LANDSLIDE FAILURES Prior to specifically discussing the study site conditions and findings, a review of the general background of slope stability and landslides in the southern Puget Sound will be presented to provide a context for evaluating this site. First, it should be understood that the two main elements responsible for the development of slope instability are gravity and water. Gravity provides the driving force,which has increasing impact with steepening slopes. Water increases soil weight, reduces soil strength, and lubricates the internal soil structure, and eroding surficial soil. The interplay of these elements is dynamic, changing dramatically with time. Minor changes in the balance of these conditions, natural or human generated, can have significant adverse impacts. Landslides are typically defined as mass downward movements of rock or soil, as a result of gravity acting upon a material mass that is in an unstable state of equilibrium. Such soil failures range in size from a few cubic feet of soil moving inches to massive movements incorporating millions of cubic yards moving hundreds of feet. Typically, landslides in soil occur in several forms: rotational slides, compound slides, falls, translational slides and debris flows. The most common forms of slides in the South Puget Sound are translational slides and debris flows, which occasionally occur together as compound slides. Due to the relatively young geologic climate in the Puget Sound and the dynamics of a coastal environment, the factors shaping the lower Sound Basin have been and still are quite active. In fact the landslide process is responsible for the slopes along the entire basin perimeter. A brief study of the Slope Stabilty Map of Thurston County, Washington (Geologic Map GM-15) published by the Washington State Department of Natural Resources in 1976 indicates that 80% of the Thurston County Puget Sound frontage is Class 3 —Unstable as a result of poor underlying soils, steep slopes or active slide conditions. The remainder of the shoreline is Class 2 — Stable under natural conditions, becoming unstable if disturbed, or subject to liquefaction. Hence, when considering slope stability along any Puget Sound Marine Bluff, the question is not "Has this slope experienced a landslide?", but"How big, how close and how often do landslides occur?" Finally, although minor landslides and slope failures occur regularly, major landslide activity in the lower Puget Sound is cyclic. The cycles tend to follow the wet season rainfall pattern. In the recent past, extreme water (high rainfall) years occurred in the early 1950's, mid 1970's and late 1990's. Both periods were accompanied by major landslide occurrences along the Puget Sound and surface expressions of shallow groundwater in central and southern Thurston County. Robinson vs Peeples-Residential Site Slope Failure/Stobility Page 1 JWM&A N01107 218/02 J 3' �;� :,s•aJ-'tee.•-'r-� ,.�`t •- _+,,,��,;,'•; Sid � tr„-4s' aS�i! �n�:=_'-.-� .� •t `' - ��Ll •- i. � _..��'�`�•y'i �rF�tis�•~ ~ ..��.. •�, 'r '' t l.r' �t t t t t •1 � .(�• '_�+�T'-:'e ,,ate, s'1!\t_ }b�s�;,_ _�^Mf.'A �--�' ♦ - � i,�R ..j. � j >'�►. •� '�tip. a. .�� - r. - Quake Forecast Shifts t0 Land [NORTHWEST SCIENCE REPORTER Scientists say data show the heart of INS AGU PRIZE a huge disaster under the Coast Range chard L. Hill, science reporter for The Oregonian, has and the western Willamette Valley on an American Geophysical Union 2000 award for sci- ence journalism. Tuesday May 4, 1999 Hillis the first winner of AGU's new David Perlman By Richard L. Hill of The Oregonian staff Award for Excellence in Science Writing—News for his ©1999 by The Oregonian, Portland, Oregon story, "Quake Forecast Shifts to Land", published May 4, Used by permission 1999.The Perlman Award is named for the science editor of The San Francisco Chronicle. who was the 1997 winner of AGU's Sustained Achievement Award in Science Writing. SEATTLE — New research indicates that a massive earth- Hill's story, which was published at the top of page one in quake could occLrr directly underneath the Oregon Coast Range The Oregonian, reported new research that concluded that and the western portion of the Willamette Valley. western Oregon could be the epicenter ofa"colossal"earth- For nearly 15 years, scientists have warned that a magni- quake of magnitude 8 or 9. Previous estimates had sug u - tude 8 or 9 earthquake could strike about 30 miles offshore and gested that'sch a quake could occur some 30 miles off- rock the coast,causing severe shaking and huge tsunamis. shore, causing much less potential damage. The story is However, recenfdata gathered from satellites by scientists at available at http://www.ore2onlive.com/news/99/05/ Oregon State University and three other institutions show that st05O4O8.html. the colossal quake could hit much farther inland and cause The Perlman Award consists of a plaque and S2,000.An more severe damage to a larger area—including the more pop- independent committee of scientists and journalists recom- ulated cities of the Willamette Valley such as Portland, Salem mends the winner to the AGU Council, whose Executive and Eugene. Committee makes the final decision.The Perlman Award is No one knows when such an earthquake might strike the for stories written under deadline pressure of one week or Northwest, but the geologic evidence suggests that such less. Work prepared for any medium except books is eligi- quakes occur about every 400 years, plus or minus 200 years. ble. Hill will receive his award at the AGU Fall Meeting in The last major earthquake on the Oregon coast—believed to be San Francisco. California, in December. a magnitude 9—occurred 300 years ago, previous studies showed. Chris Goldfinger, a marine geologist at OSU, and his col- leagues will present their findings today in Seattle at the annual To come to this new conclusion, the scientists used the sat- meeting of the Seismological Society ofAmerica.They also re- ellites of the Global Positioning System to detect extremely ported the results recently to the Oregon Seismic Safety Advi- small movements of the Earth's surface in an area from the sen- sory Committee. tral Oregon coast into the central Willamette Valley. Two per- The research team found that the locked portion of the Cas- manent GPS receivers in Newport and Corvallis monitormove- cadia Subduction Zone—where the eastward-moving Juan de ment full time,while other receivers were taken to several sites Fuca Plate plunges under the western-moving North American to measure yearly movement. Plate—extends beneath the Coast Range and as far as the west- The researchers expected to find little movement because ern side of the Willamette Vallee.The locked zone probably is of the lack of earthquakes and previous data that showed little wider than previously thought.although the new data give less uplift in central-western Oregon.something commonly associ- information about the width. ated with a locked Subduction fault. EARTHQUAKE POTENTIAL MOVES INLAND I Research suggests that the locked zone of the Juan de Fuca and North I • d _ American plates is larger than thought.A previous model showed the I Portland �;pacific locked portion of the Cascadia Subduction Zone as being offshore.The r I j. Study /;Ocean c A, new model shows the locked zone extending farther inland. few ort /� I' i area7de Study Coast Coast Cascades o I Corvallioil, % / H Juaarea Old zone Range I Willamette Valley •� / Fuc I a Old zone Ef I vrE. North I I 1�co", North 777 American I PacificlAmerican Juan de :.- Plate_14Coos Bay � PlatePlateorda FucaPlate I New zone i U 'Plate C _'F. Man•;?sins FaL Source:Oregon State University MICR-_-L MODE/THE OREGONIAN 22 Ilashington Geology, col. 28, no. 1/2, September2000 f of - Instead,they found that the ground is moving nearly half an '.1700,and large quakes appear to have struck about_1,100 years r inch a year toward the northeast. The rapid velocity worries ago, 1,300 years ago and 1,700 years ago. earthquake researchers and indicates that the underlying plates Curt D. Peterson, a professor of geology at Portland State are locking up rather than sliding by each other,resulting in in- University who has uncovered many of the buried marshes credible strain. along the Northwest coast,said the new research supported his As the Juan de Fuca Plate presses forward to the northeast decade-old theory that the locked zone might be twice as wide- in the locked zone,it causes the piggybacking North American as thought and capable of generating a huge quake. Plate to bulge upward and inland toward the northeast. The "I hope this new evidence is going to help planners and gov- pressure continues to build for years until an earthquake un- ernment agencies get back on track about the seriousness of the leashes the stress in one powerful jerk,causing the bulge to col- hazard. The metro areas such as Seattle and Portland need to lapse and forcing the area to drop instantly. examine what a magnitude 9 means in terms of the whole re- "We were very surprised by the results we got," said gion going all at once,"Peterson said. Goldfinger, an OSU assistant professor of oceanography. "It Mark Darienzo,earthquake and tsunami program coordina- was quite different from what we expected. We thought this for for the Oregon Office of Emergency Management,said the would be an area that would show little. if any, movement." study supported concerns that a huge subduction-zone earth- The half-inch of movement each year is imperceptible,but quake "is not just a coastal problem, but could be an inland the accumulated pressure that has been stored since the last ma- problem as well." jor earthquake in 1700 can only be unleashed in an earthquake. "More research is needed." Darienzo said, "but these new "That means there's been 300 years of strain that will be re- findings show that the potential for such a quake can't be over- leased,"said John L. Nabelek,a seismologist and OSU associ- looked—it shouldn't be just tossed aside." ate professor of oceanography who participated in the study. You can reach Richard L.Hill at 503-221-8238 or by e-mail "And"And it's not just the proximity of the strain to larger cities that at richardhillCnews.oregonian.com. is a concern,but we've found that the surface area of the entire locked zone is much larger than previously thought. That means a larger quake." This story it-as briefly updated in a longer story summari_- Goldfingersaid the data stuggest that the two plates are"es- ilia all kinds of other research about the Cascadia Subduction sentially bolted together—they're 100 percent coupled. zone, i»cltrdirng archaeological studies. It ran on Jan. 26, ''In addition, the Coast Range is an extremely strong. rigid ?000,the300th anniversarl•of thelastareatquake. Thefollow- block of rock that is more than capable of accumulating the sort ilia is the pertinent excerpt fr•orrr the Jan. 26 sto,•i•: of energy you need for a large earthquake." McCaffrey. Goldfinger and the other researchers are ana- Other scientists involved in the study included Robert lyzing more extensive GPS data they collected last summer. McCaffrey, an associate professor of earth and environmental "The new data might change the picture about the locked zone science at Rensselaer Polytechnic Institute in Troy, N.Y., and somewhat."Goldfinger said.--It's a eery complicated problem, Mark Murray of Stanford University. The work-was conducted and it's going to take a while to sort this out."■ in cooperation with Curtis L. Smith of the National Geodetic ` Survey in Salem. Will Prescott of the U.S. Geological Survey supplied previous GPS measurements that improved the re- sults. MOUNT BAKER/GLACIER PEAK The new findings have made Goldfineer, who in previous COORDINATION PLAN years argued that the largest subduction zone quake was more Mount Baker and Glacier Peak volcanoes in northwest Wash- likely to be a magnitude 8 than a 9, rethink his theory. '-This ington have each erupted within the last three centuries. Al- changes my views 180 degrees,"he said."The whole argument though neither mountain shows signs of unrest that might lead for an 8 rather than a 9 disappears." to renewed eruptive activity. Glacier Peak did produce one of Although quakes of either size would be devastating.steak- the largest explosive eruptions of any Cascade volcano in the ing from a magnitude 9 event would last two to three minutes— past fifteen thousand years and future eruptions at either volca- about twice as long as the shaking a magnitude 8 quake would no could cause significant disruption in nearby drainages and produce. dowmvind areas. Researchers elsewhere in the Northwest have come up%%.ith To prepare for future unrest, emergency managers from similar results using the satellite-based Global Positioning Snohomish,Skagit,and Whatcom Counties,representatives of System. The locked zone between the plates extends farther the State of Washington(Departments of Emergency Manage- landward beneath Washington and Southern Oregon as well, 1-1 ment and Natural Resources) and the Province of British Co- and a little farther under Vancouver Island than previously lumbia, as well as personnel from the U.S. Forest Service and thought. U.S. Geological Survey are working together to produce a A largerresearch effort,planned next year,will examine an Mount Baker/Glacier Peak coordination plan. area from Northern California to Canada, including Portland. The purpose of the plan is to coordinate the actions that var- TheCascadia Subduction Zone is a 750-mile long fault that ious agencies must take to minimize loss of life and damage to runs 60 to 150 miles offshore from British Columbia to North- property before,during.and after a hazardous geologic event at ern California. Similar subduction zones have produced the either volcano. The plan strives to assure timely and accurate two largest recorded earthquakes in the world—a magnitude dissemination of warnings and public information and also in- 9.5 quake on the coast of Chile in 1960 and a magnitude 9.2 eludes the necessary authorities as well as statements of re- quake in southern Alaska in 1964. sponsibilities of county,state,and federal agencies in the U.S. No quakes of that size have been measured in Oregon's and Canada.A similar response plan has been produced by the brief recorded history,but evidence from buried marshes along Mount Rainier Volcanic Hazards Work Group for Mount the coast indicate that such events occurred at least seven times Rainier volcano. in the past.3,000 years. The last one hit the coast in January Washington Geology, vol. 'S, no. 112. September 2000 23 �� - i ice• °�l r•f:'���"�' . s • A• jr[ L Ll ' • :��•�`•'yam,,r� :, Q a ':• .. `5 T1 -^41't' '6,s� .r�i L2 •`may +'_,,: --'� .�: -. (Lai. i�:r 'ti r� .. �• - How We Measure an Earthquake--Magnitude and Intensity Magnitude is a measure of the strength of an magnitude of an earthquake is determined from earthquake or strain energy released by Describing Magnitude the logarithm of the amplitude of waves re- fit, as determined by seismographic observa When scientists refer to a corded by seismographs. Adjustments are in- tions.This is a logarithmic value originally de- "great"earthquake,they do not cluded for the variation in the distance between fined by Charles Richter (1935). The Richter mean the earthquake was fabu- the various seismographs and the epicenter of Scale is not used to express damage. An earth- tous,they mean it was huge.In- the earthquakes. On the Richter Scale, masts quake in a densely populated area, which re- formally,earthquakes are clan-y rude is expressed in whole number and Ueci- - sults in man deaths and considerable damage, shied according co their magni rude size: mal fractions. For example, a magnitude 5.3 may have the same magnitude as a quake in a might be computed for a moderate earthquake, remote area that does nothing more than under 5.0 small and a strong earthquake might be rated as mag- frighten the wildlife. 5.0-6.0 moderate nitude 6.3. Becautse of the logarithmic basis of Intensity is,a measure of the effects of an 6.0-7.0 large the scale, each whole number increase in mag- earthquake at a.particular place on humans, 7.0-7.8 major nitude(for example,from 4.6 to 5.6)represents structures and(or)the land itself.The intensity 7.8+ great a ten-fold increase in measured wave ampli- at a point depends not only upon the strength of rude on a seismogram. As an estimate of en the earthquake (magnitude) but also upon the Front the U.S. Geolog!caf Sur- vet [hup://ww�c.scecdc.scec. ergy,each whole number step in the magnitude distance from the earthquake to the point and orcr!egcounirv.html] -scale corresponds to the release of about 30 the local geology at that point. times more energy than the amount associated =with the preceding whole number value. The Richter Magnitude Scale In other words, a magnitude 6.7 earthquake releases over Seismic waves are the vibrations from earthquakes that travel 900 times (30 times 30) the energy of a 4.7 earthquake—or it through the Earth. They are recorded on instruments called takes about 900 magnitude 4.7 earthquakes to equal the energy seismographs. Seismographs record a zigzag trace that shows released in a single 6.7 earthquake! There is no beginning or the varying amplitude of ground oscillations beneath the in- end to this scale. However,rock mechanics seems to preclude strument(Fig. 1). Sensitive seismographs,which greatly niag- earthquakes smaller than about-1.0 or larger than about 9.5. A nify these ground motions,can detect strong earthquakes from magnitude-1.0 event releases about 900 times less ever;-. : .1❑ sources anywhere in the world.The time,locations,and magni- a magnitude 1.0 quake. Except in special circumstances,earth- tude of an earthquake can be determined from the data re- quakes below magnitude 2.5 are not generally felt by humans. corded by seismograph stations. Earthquakes with magnitude of about 2.0 or less are usually The Richter magnitude scale was developed in 1935 by call microearthquakes. They are not commonly felt by people Charles F. Richter of the California Institute of Technology as and are generally recorded only on local seismographs.Events a mathematical device to compare the size of earthquakes.The with magnitudes of about 4.5 or greater—there are s-, eral thousand such shocks annually worldwide—are strong enough File 010206e.rse to be recorded by sensitive seismographs all over the :�:orld. Stan:2/116/01 22.29.17 UTL(l)Sleeen:Rasie(Udine)116.9i�N 11 ME Semplr.s:7150 SPS:2S Comm ent 6/115129km:46 Rai/La, 44.2.8YE ern OelyT]Pn2431i MVSEA Mnx/Gin:]28I/-NIIJC N6 Y:xl Great earthquakes,such as the 1964 Good Friday earthqu ,- In Event Time:OZJ06 22:28:�6 0 LaVlang�11.211 B.IE DopIA:1?.m 21.9mi Meg-A01.5 l�"= Org:22.28.11 5 P 22:29.11.1 S:22.10']2;a DiM:15.7—Dig::]d0ldeg 122.6km 262.Smi Meg:M14 S U91:10 1000;....;.._.;_....:.....:.....:.....;....;....,....;..........:.....;.....:..... Alaska,have magnitudes of 8.0 or higher. On the average,one earthquake of this size occurs somewhere in the world each 3000 ---- ........ year.Although the Richter Scale has no upper limit, the largest known shocks have had magnitudes in the 8.8 to 8.9 range.Re= 2ndU;.... .... .... ...........' ....: .. .. .. .. Gently, another scale called the moment h magnitude scale as , loon; been devised for more precise study of great earthquakes. l �. 2 The Modified Mercalli Intensity Scale '' The effect of an earthquake on the Earth's surface is called 7'le P ;l� '"" """"?""""?'""" intensity.The intensity scale consists of a series of cert: 2000 i .;..... responses such as people awakening, moement of furniture, ,....,.... . v.. :...... da mage to chimneys, and finally—total destruction. Although ,gug ..-" .... .... numerous intensity scales have been developed over the last nu several hundred years to evaluate the effects of earthquakes, Icon .••• .••. ••.•%... the one currently used in the U.S. is the Modified itfercalli In- 22.29.17 29.57 90:17 31:17 3I:S7 32 77 ]]'17 tensity Scale (Iv IMI). It was developed in 1931 by the Ameri- Figure I. Seismogram of the Nisqually earthquake from a station in can seismologists Harry Wood and Frank Neumann. This; northern Italy.Frequently a more complete record can be obtained from scale, composed of 12 increasing levels of intensity that range stations further away from a large quake.'P'indicates the arrival of the from imperceptible shaking to catastrophic destruction s des- P-wave, a compressional wave that travels fast, and the 'S', the S- ignated by Roman numerals. It does not have a mathea::.::;,a1 wave,a shear wave that is slower but larger and does most of the dam- basis; instead it is an arbitrary ranking based on observed ef- age. Rapid shaking dies off quickly with distance, so nearby earth- s. quakes are 'jolting'and far away earthquakes are'rolling'. Duration of fec T the shaking increases with the magnitude of the earthquake. The Modified Mercalli Intensity value assigned to a spe- Seismogram downloaded from http://www.seismicnet.com/ cific site after an earthquake has a more meaningful measure of q u ai.e a'Q 102/. .cvc liv to 01C nonscleWlst than tI1C!11?/'n1!!!(l L' hecm!�- i11ten_ 20 Washinarnn Gvnlnav vn/ 'R nn 3 Adnv 7047 Table 1. Magnitudefintensity comparison.Magnitude and intensity measure different characteristics of earthquakes.Magnitude measures the en- ergy released at the source of the earthquake.Magnitude is determined from measurements on seismographs.Intensity measures the strength of shaking produced by the earthquake at a certain location.Intensity is determined from effects on people,human structures,and the natural environ- ment. The table below gives intensities that are typically observed at locations near the epicenter of earthquakes of different magnitudes. Down- loaded from http://neic.usgs.gov/neis/general/handouts/mag_vs-int.html. Richter M NII magnitude equivalent Modified Mercalli Intensity Scale(NMI) 1.0-3.0 I 1. Not felt except by a very few under especially favorable conditions. 3.0-3.9 If-Ill 11. Felt only by a few persons at rest,especially on upper Floors of buildings. 111. Felt quite noticeably by persons indoors,especially on upper floors of buildings.Many people do not recognize it as an earthquake.Standing motor cars mayrock slightly. Vibrations similar to the passing of a truck. Duration estimated. 4.0-4.9 IV-V IV. Felt indoors by many,outdoors by few during the day.At night,some awakened. Dishes,windows,doors disturbed; walls make cracking sound.Sensation like heavy truck striking building.Standing motor cars rocked noticeably. V. Felt by nearly everyone;many awakened.Some dishes,windows broken. Unstable objects overturned. Pendulum clocks may stop. 5.0-5.9 VI-VII VI. Felt by all.many frightened.Some heavy furniture moved;a few instances of fallen piaster. Damage slight. V11. Damage negligible in buildings of good design and construction;slight to moderate in yell-built ordinary structures; considerable damage in poorly built or badly designed structures;some chimneys broken. 6.0-6.9 VII-IX Vlll. Damage slight in specially designed structures;considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures.Fall of chimneys,factory stacks,columns,monuments.walls.Heavy furniture overturned. IX. Damage considerable in specially designed structures;well-designed frame structures thrown out of plumb. Damage great in substantial buildings.with partial collapse. Buildings shifted off foundations. 7.0 and Vlll or X. Some well-built wooden structures destroyed;most masonry and frame structures destroyed with foundations. Rails bent. higher higher XI. Few,if any(masonry)structures reatain standing.Bridges destroyed. Rails bent greatly. XII. Damage total.Lines of sight and level are distorted.Objects thrown into the air.- sity refers to the effects actually experienced at that place- Af- higher numbers of the scale are based on observed structural ter the occurrence of widely felt earthquakes,the U.S.Geologi- damage. Structural engineers usually contribute information cal Survey mails questionnaires to postmasters in the disturbed for assigning intensity values of VIII or above. area requesting the information so that intensity values can be Although they measure different characteristics of an assigned. The results of this postal canvass and information earthquake,the Richter Scale and the Modified Mercalli Inten- furnished by other sources are used to assign an intensity sity Scale can be roughly equated near the epicenter as Shown within the felt area. The maximum observed intensity gener- in Table 1. ally occurs near the epicenter. Ibrid�zd fion: "Tire Severity ofan Earthquake". The lower numbers of the intensity scale generally deal 1'. S. Geoloaical Survev General l,rterest Publication. ith the manner in which the earthquake is felt by people. The p.hu,rl WASHINGTON DIVISION OF GEOLOGY EARTHQUAKE HAZARD MAPS AVAILABLE Preliminary maps of liquefaction susceptibility for the Renton by J. D. Dragoyich and P. T. Pringle, 1995. Washington Division of and Auburn 7.5' quadrangles. Washington, by S. P. Palmer, 1992. Geology and Earth Resources Geologic Map GPI-44, l sheet, scale Washington Division of Geology and Earth Resources Open File Re- 1:24,000, with 26 p. text. S2.32 - .I S tax (Wash. residents only) _ port 92-7,24 p., 2 plates. Free S2.50. Liquefaction susceptibility for the Des Moines and Renton 7.5- Geologic folio of the Olympia-Lacey-Turnvya ter urban area. minute quadrangles, Nashington, by S. P. Palmer, Henry W. NVashinaton-Liquefaction susceptibility neap.by S. P. Palmer,T. Schasse, and D. K. Norman, 1994. Washington Division of Geology J. Walsh,and W. G. Gerstel, 1999. Washington Division of Geology and Earth Resources Geologic Map GM-41, 2 sheets,scale 1:24,000, and Earth Resources Geologic \lap G\i-47. 16 p., l plate, scale with 15 p. text. S3.71 +.29 tax(Wash. residents only)=S4.00. 1:48,000.S2.32 -AS tax(Nash.residents only)=S2.50. Relative earthquake hazard ntap for the Vancouver,Washington, Tsunami hazard map of the southern Washington coast- urban region, by NI. A. Nlabe,..I. P. ivfadin, and S. P.Palmer, 1994. i•lodeled tsunami inundation from a Cascadia subduction zone Washington Division of Geology and Earth Resources Geologic Nlap earthquake, by T. J. Walsh. C. G. Caruthers. A. C. Heinitz, E. P. GM-42, 2 sheets,scale 1:24,000.with 5 p.text. Free. Nlyers IN,A.i\l. Baptista.G.B.Erdakos.and R.A, Kamphaus,2000. h Bay' 7.5- Washington Division of Geology and Earth Resources Geologic Nlap Liquefaction susceptibility for the Auburn and Poyer minute quadrangles, Nashington,by S. P. Palmer, T. J. Walsh, R. GNI-49, 12 p., 1 plate, scale 1:100,000. S3.71 - .29 tax (Wash. resi- L. Logan,and W. J. Gerstel, 1995. Washin.-ton Division of Geology dents only)=S4.00. and Earth Resources Geologic Map GM-43, 2 sheets, scale 1:24,000, (Our address and phone number are on p.3. Orders must be prepaid. syith 15 P.text. S4.63 +.37 tax(Nash. residents only)=S5.00. ,Make check ornro,ev order parable to the Department ofrVatural Re- Liquefaction susceptibility for the Sumner 7.5-minute quadran- sources. Taxes apple• to Washington residents otlt•. Please include g1e, Washington, iyith a section on liquefaction, by S. P. Palmer, S1.00jbrpostaaeandhandlingvfoders to be sent brmail.) Washington Geologt•. vol. 28, no. 3. :May 2001 21 Tertiary Andesitic Lava-flow Complexes ,(Stratovolcanoes) in the Southern Cascade Range of Washington-0 bservations on Tectonic Processes within the Cascade Arc Paul E. Hammond Department of Geology A 51ON Portland State University Portland, OR 97207-0751 3 Mount Meager Mount Clayley � Mount Garibaldi INTRODUCTION EXPLORER BC The Cascade Volcanic Arc PLATE vANCoUV __ _._._.__._.__._.-.__ - Sovanco �� Mount Baker WA ID According to plate tectonics theory, Fracture Nootka subduction of the ocean floor beneath Zone Fault t 'i Glacier Peak an adjacent continental margin pro- Cobb .m I40 SEATTLE duces a trench off the coast and genet- Fracture o m SVVC m N a r SWCC Figure 3 ates magma at depths between 80 andLIJ a� Zone N i 60 Mount Rainier d 270 km (Gill, 1981 ; Tatsumi and Eaains, 1995). This magma rises �� 4.7cm�y, t Goat Rocks �( X Mount through continental crust to erupt at the m l Adams Mount surface and form a chain of volcanoes, Cascadia : o l St.Helens v c Basin I ---- defining an arc. Most continental mar- �� ; e ; PORTLAND Mount Hood W AN DE FUCA m gin arcs surrounding the Pacific Ocean JU C t of � t are 50 to 275 km in width and lie 125 to PLATE U. <c Mount Jefferson e Blanco Fracture 0i Three Fingered Jack c 250 km landward of their associated Mountwashington trenches or subduction zones (Moore, Zone Three Sisters Broken Top = Mount Bachelor 1982, Gill, 1981;-Tatsumi and Eggins, 3.a c^tlyr Ca Diamond Peak o 1995).The trenches lie 1,300 to 13.500 km from the East Pacific Rift (spread Mount Bailey�Mounr Crater Lakak- en ing center).The oceanic plates subduct PACIFIC Ci . �Ntount McLoughlin OR at angles increasing to 30 to 60 degrees PLATE a" MEDFORD ■ at depth and at rates of 4.1 to 10.8 cm/yr CA NV (41-108 km/m.v.).The volcanoes clos- o� count . est to the trench are larger, closer GORDA Shasta — N spaced (30 to 60 km apart), and most PLATE i 0 200 magmatically productive in the chain. ,40 1 60 LPG' t kilometers 40ON These volcanoes delineate a volcanic Mendocino Fracture Zone front that is aligned parallel to the strike s SACRAMENTO of the subducting plate. Inland from the front,the volcanoes decrease in number B JUAN DE FUCA?LATE NORTH AaR-ARC PLATE andproductivity, are more widely T2ENCR•—FORFast caR-ARC a+cxARc spaced, and may form a belt containing X de Fuca Cascadia Basin sb sh cRa Range PS SH A Columbia Vf X' a minor chain. ^ zs- ___ ____ continental crust 2___�25 The Cascade arc differs in some fea x 50- oceanic mst �a so11 tures from other arcs of the Pacific �100i oceanic lithosphere ���, magma 100 Rim.It is 50 km in maximum width and o ��:b:gezone°n 3 lies 250 to 350 km east of the Cascadia I mantle �� mantle subduction zone(Fig. I A).The subduc- tion zone lies only 50 to 450 km from Figure 1. A.Simplified map of the Cascade arc,its major volcanoes(A).-44*,spreading ridge the Juan de Fuca—Gorda spreading (center)with direction of movement of oceanic plates;—*,convergence direction and rate of oce- ridges, and the plates subduct at only anic plate;i, subduction zone with barbs in direction of subduction;/4o,contour on subducting 3.4 to 4.7 Cm/yr (Riddihough, 1984; plate with depth in kilometers; SWCC, southern Washington Cascades conductor; vf, volcanic front. (Modified from Hammond, 1989.) B. Cross section X—X' through Cascadia subduction Duncan and Kulm, 1989). Geophysical zone,Mount St.Helens(SH),and Mount Adams(A).Note that plate flattens between 40 and 60 km studies, summarized by Finn (1990), depth. a, 20°-dip projection of subducting plate from 60 km depth; b, projection of subducting have identified the top of the subduct- plate at 600 dip;c,coast;CaR,Cascade Range(arc);pb,plate boundary;PS, Puget Sound—Wil- ing plates to a depth of 60 km at the lamette Valley trough; sh, edge of continental shelf; sl, foot of continental slope; SL, sea level. -northern and southern ends of the arc (Modified from Finn, 1990,and Weaver and Baker, 1988.) • . . — , -,I I ._-:I Irmo but not beneath the volcanoes. At this depth the plate dips at an number of volcanoes and their concentration and to delineate average of 20 degrees eastward, flattening between 40 and 60 any volcanic fronts.Because the volcanic front is parallel to tl• km depth (Fig. 1B). Below 60 km depth the plate dips more trench, it is a tectonic line. If an alignment of older volcano( steeply, possibly 45 to 60 degrees, to a depth of at least 80 km can be recognized, it becomes a reference to determine if the in order for magma to be generated. arc has been deformed.Because the volcanoes can be radiomet- In the Cascade arc (Fig. I A), the volcanoes delineate a dis- rically dated,the rate of deformation can also be determined. continuous volcanic front from (✓fount Meager in British Co- an ancient volcanic front is no longer parallel to the trench,tt lumbia south to Lassen Peak in California. A few minor volca- arc has probably rotated from its former location. (See Wells, noes (not shown) in southern Oregon and northern California 1990.)If the volcanic front is offset,then the arc may have bee might be considered lying either trenchward or inland from the deformed internally. However, this investigation is beset wit volcanic front.Overall,the Cascade arc is a single chain of vol- unresolvable problems, as discussed below; nevertheless, ;t canoes, with possibly the greatest average spacing between gives further insight to the tectonic processes affecting the arc volcanoes, 70 ±43 km (determined from the 23 volcanoes in since its inception. Fig. IA), in all the Pacific Rim arcs. The width of a volcanic are(belt) is generally inversely re- ANDESITIC LAVA-FLOW COMPLEXES lated to the angle of subduction (Tatsumi and Egains, 1995). Stratovolcanoes and Where the angle is greater than about 30 degrees, and espe- cially where it approaches 60 degrees,a single,narrow chain is Andesitie Lava-Flow Complexes developed. And where plate convergence rate is high, more On the basis of my mapping(Hammond, 1963, 1980, 1995-97, than about 6 cm/yr,the angle of subduction tends to be steeper. unpub.mapping; Hammond and others, 1994),stratovolcanoe! Other factors can affect the angle of subduction.Thickening of were the chief eruptive centers that contributed most rock prod the overriding continental plate by underplating or compres- ucts in the 7- to l0-km thickness of volcanic strata underlying lion can steepen the angle. Thinning of the plate by extension the range(Smith, 1993; Evarts and Swanson, 1994). Similarly, can lessen the angle. As the distance between trench and Gill(1981)and Tatsumi and Eggins (1995) found that the moss spreading rift decreases,as in the case of the Cascadia subduc- common volcanoes in arcs are stratovolcanoes. tion zone, the temperature of the subducting oceanic plate in- Most stratovolcanoes are composed of three parts (Fig. creases and therefore its density decreases, making the plate 2A),a central cone of largely fragmented debris,a lower encir- more buoyant and lessening the angle of subduction. cling apron of chiefly lava flows, and an outer low-lying skirt In summary, the Cascade arc is among the narrowest, its of chiefly volcaniclastic deposits, including laharic, air-fall, volcanoes most widely spaced and least productive (fortu- pyroclastic-flow, and volcanic sedimentary deposits, which nately for Pacific Northwest inhabi- tants). Its subduction zone lies rela- ACONE(S) tively close to a spreading rift. And its APRON chiefly ruffs,breccia,minor lava flows —1,000— oceanic plates subduct at a low angle at Chien lava flows 1,500 m ' r y —, slope break about the slowest rate of convergence. ssclRT eccentriccone(s) With breakup of the Juan de Fuca plate volcaniclasticdeoosits, margin of possible caldera into the smaller Gorda and Explorer r tuffs,and lavafiows plates and eventually into other small ________________________ plates, these conditions may presage the demise of the Juan de Fuca plate, the Cascadia subduction zone (Riddi- plug(s),dike(s) volcaniclastic crosioa surface volcaniclastic hough, 1984), and the cessation of Cas- B deposits deposits Cade arc volcanism. Over its 40± m.y. LAVA-FLOW COMPLEX history, the Cascadia subduction zone has changed from rapid, 8.4 cm/yr, to slow plate convergence (Duncan and C Kulm, 1989),and possibly from a steep szo^io ofara ROtratovolcano CandE angle of subduction to relatively shal- centraldeposiu, low subduction. The Cascade arc may 1-sue have changed from a wide belt to a nar- -1%ofarea row arc, from high magmatic produc ofstratavolcano tivity and abundant volcanoes to re- y=� duced activity and few volcanoes. And ' its volcanic front possibly migrated eastward with development of succes- LAVA-FLOW COMPLEX sive volcanoes to its present location. SKIRT Purpose In order to investigate this possible ,Y (farther if most evolution and to compare a segment of distantashfall proximal deposits the older arc with the present arc, I lo- included) cated volcanoes in the older volcanic 00%of ama of stratovolcano distal deposits possible total aa-1,000-5,000km= terrain of the Cascade Range in south- Figure 2. Profile and areal sections of(A)a stratovolcano,•(8)its lava-flow complex after erosion ern Washington to determine the of the volcano, and (C) areal dimensions of the stratovolcano and its deposits.