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Geology, Mineral Resources and Hazardous Materials Technical Background Report MARIN COUNTYWIDE PLAN Geology, Mineral Resources and Hazardous Materials Technical Background Report Alex Hinds, Community Development Director Michele Rodriguez, Principal Planner, AICP Frederick Vogler, GIS Manager Dan Dawson, Senior Planner Kristin Drumm, Planner Don Allee, Clerical Support Special Consultants: Snyder and Wilson Engineering, Inc. 360 Grand Avenue, #115 Oakland, CA 94610 Nichols • Berman 110 East D Street, Suite E Benicia, CA 94510 March 2002 Updated November 2005 The Marin County Community Development Agency, Planning Division 3501 Civic Center Drive, San Rafael, CA 94903 This page intentionally left blank. GEOLOGY, MINERAL RESOURCES AND HAZARDOUS MATERIALS TABLE OF CONTENTS I. PURPOSE AND EXECUTIVE SUMMARY..............................................................1 II. GEOLOGIC LEGISLATION.....................................................................................1 A. ALQUIST-PRIOLO EARTHQUAKE FAULT ZONING ACT ..................1 B. SEISMIC HAZARDS MAPPING ACT ..........................................................2 1. Purpose and Programs.................................................................................2 2. Guidelines for Mitigation.............................................................................4 C. GEOLOGIC HAZARD ABATEMENT DISTRICTS (GHAD) ...................4 D. SUMMARY AND ISSUES TO CONSIDER..................................................5 III. GENERAL GEOLOGIC SETTING...........................................................................5 A. REGIONAL TECTONIC FRAMEWORK AND GENERAL GEOLOGIC HISTORY...................................................................................5 B. GEOLOGY EAST OF THE SAN ANDREAS FAULT ZONE ..................10 1. Bedrock .....................................................................................................10 2. Surficial Deposits .......................................................................................11 C. GEOLOGY WEST OF THE SAN ANDREAS FAULT ZONE.................11 1. Bedrock .....................................................................................................12 2. Surficial Deposits .......................................................................................14 D. GEOLOGIC UNITS WITHIN THE SAN ANDREAS FAULT ZONE ...14 E. SUMMARY AND ISSUES TO CONSIDER................................................14 IV. FAULTING AND SEISMIC HAZARDS .................................................................15 A. ACTIVE FAULTING AND FAULT RUPTURE ........................................15 B. SEISMICITY ...................................................................................................18 C. GROUND SHAKING AND SHAKING SUSCEPTIBILITY ....................21 1. Hazard Description ...................................................................................21 Geology, Mineral Resources and Hazardous Materials Updated November 2005 i MARIN COUNTYWIDE PLAN 2. Hazard Mitigation ..................................................................................... 24 D. LIQUEFACTION SUSCEPTIBILITY........................................................ 26 1. Hazard Description................................................................................... 26 2. Hazard Mitigation ..................................................................................... 29 E. TSUNAMIS AND SEICHES ........................................................................ 29 1. Hazard Description................................................................................... 29 2. Hazard Effects and Potential..................................................................... 29 3. Tsunami Hazard Mitigation...................................................................... 31 F. EARTHQUAKE INDUCED LANDSLIDES .............................................. 31 G. SUMMARY AND ISSUES TO CONSIDER ............................................... 32 V. SLOPE STABILITY AND LANDSLIDING........................................................... 33 A. HAZARD DESCRIPTION........................................................................... 33 1. Falls ........................................................................................................... 34 2. Topple....................................................................................................... 34 3. Slides ......................................................................................................... 34 4. Lateral Spreads.......................................................................................... 35 5. Flows ......................................................................................................... 35 B. HAZARD POTENTIAL ............................................................................... 35 1. Novato Area.............................................................................................. 35 2. Southeastern and Central Marin County .................................................. 36 3. Western Marin County............................................................................. 37 4. Countywide Landslide Potential ............................................................... 37 C. HAZARD MITIGATION............................................................................. 41 1. Reasons for Mitigation .............................................................................. 41 2. Methods of Mitigation............................................................................... 42 D. SUMMARY AND ISSUES TO CONSIDER ............................................... 43 VI. EXPANSIVE AND CREEPING SOILS .................................................................. 44 A. HAZARD DESCRIPTION........................................................................... 44 B. HAZARD MITIGATION ............................................................................. 46 C. SUMMARY AND ISSUES TO CONSIDER ............................................... 46 ii Updated November 2005 Geology, Mineral Resources and Hazardous Materials GEOLOGY, MINERAL RESOURCES AND HAZARDOUS MATERIALS VII. GRADING................................................................................................................47 A. INTRODUCTION .........................................................................................47 B. TYPES OF GRADING...................................................................................48 1. Minimal Grading........................................................................................48 2. Mass Grading.............................................................................................48 C. HISTORY OF GRADING CODES ..............................................................48 D. GRADING CODE ADMINISTRATION AND ENFORCEMENT ..........48 E. GRADING INSPECTION AND THE REVIEW PROCESS .....................49 F. CONSULTING REVIEWERS ......................................................................49 G. SUMMARY AND ISSUES TO CONSIDER................................................49 VIII. SUBSIDENCE AND DIFFERENTIAL SETTLEMENT.....................................50 A. HAZARD DESCRIPTION............................................................................50 B. HAZARD MITIGATION..............................................................................50 C. SUMMARY AND ISSUES TO CONSIDER................................................51 IX. COASTAL BLUFF EROSION .................................................................................51 A. HAZARD DESCRIPTION............................................................................51 B. HAZARD MITIGATION..............................................................................52 C. SUMMARY AND ISSUES TO CONSIDER................................................53 X. STRUCTURAL HAZARDS DUE TO EARTHQUAKES ......................................53 A. HAZARD DESCRIPTION............................................................................53 1. Wood-Frame Structures ............................................................................55 2. Unreinforced Masonry Structures (URMs)...............................................56 3. Concrete Structures ...................................................................................57 4. Steel Structures ..........................................................................................57 5. Light-Gauge Steel Structures......................................................................58 B. SUMMARY AND ISSUES TO CONSIDER................................................61 Geology, Mineral Resources and Hazardous Materials Updated November 2005 iii MARIN COUNTYWIDE PLAN XI. MINERAL RESOURCES ......................................................................................... 63 A. INTRODUCTION ........................................................................................ 63 B. POTENTIAL MINERAL RESOURCE SITES ........................................... 63 1. Ring Mountain, Tiburon........................................................................... 63 2. (Sector D-1) Novato Conglomerate-Black Point ...................................... 64 3. (Sector D2) Novato Conglomerate-Black Point...................................... 64 4. (Sector I) Franciscan Complex Sandstone – San Pedro Hill.................... 64 5. (Sector J) Sonoma Volcanics Andesite – Burdell Mountain .................... 64 6. (Sector L) Franciscan Complex – Borello
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