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Preliminary Seismic Microzonation Assessment for British Columbia

Prepared by
Klohn-Crippen Consultants Ltd.
for the Earth Sciences Task Force,
Resources Inventory Committee

The Province of British Columbia
Published by the
Resources Inventory Committee


Version 1

FEBRUARY 1994


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ACKNOWLEDGMENTS

Funding of the Resources Inventory Committee work, including the preparation of this document, is provided by the Corporate Resource Inventory Initiative (CRII) and by Forest Renewal BC (FRBC). Preliminary work of the Resources Inventory Committee was funded by the Canada-British Columbia Partnership Agreement of Forest Resource Development FRDA II.

The Resources Inventory Committee consists of representatives from various ministries and agencies of the Canadian and the British Columbia governments as well as from First Nations peoples. RIC objectives are to develop a common set of standards and procedures for the provincial resources inventories, as recommended by the Forest Resources Commission in its report "The Future of our Forests".

For further information about the Resources Inventory Committee and its various Task Forces, please access the Resources Inventory Committee Website at: http://srmwww.gov.bc.ca/risc.

Earth Sciences Task Force

The background information and protocols presented in this document are based on the unpublished government report, Preliminary Inventory Manual for Sampling British...

Canadian Cataloguing in Publication Data

Main entry under title:

Preliminary seismic microzonation assessment for
      British Columbia [computer file]

Previously issued in printed format, 1994.
Available through the Internet.
Issued also in printed format on demand.
Includes bibliographical references: p.
ISBN 0-7726-3399-1

1. Earthquake hazard analysis - British Columbia.
I. Klohn-Crippen Consultants. II. Resources
Inventory Committee (Canada). Earth Sciences Task
Force.

QE535.2.C3P74 1997 551.2209711   C97-960303-X

PREFACE

This report is the result of a contract issued to Klohn-Crippen Consultants Ltd. by the Seismic Microzonation Task Group of the Resource Inventory Committee (RIC). RIC is comprised of provincial resource management ministries and appropriate federal departments. The main focus of RIC and its various task groups is to meet the challenge of sustainable development and integrated resource management in the context of providing inventory information for effective land use planning and decision making. RIC is responsible for reviewing existing resource inventory methodologies, identifying information gaps and overlaps and integrating data required for land use planning. The Seismic Microzonation Task Group was formed as a result of recognition by the RIC Earth Sciences Task Force, co-chaired by Paul Matysek and Herb Luttmerding, of an imperative need for a systematic inventory of earthquake hazards in the province. The Seismic Microzonation Task Group is coordinated by the Geological Survey Branch of the Ministry of Energy, Mines and Petroleum Resources and has representatives from the Geological Survey of Canada, B.C. Hydro, the University of Victoria, Public Works Canada, and the B.C. Ministry of Environment, Lands and Parks.

British Columbia is in a seismically active area and has had several earthquakes greater than magnitude 7.0 in the last 75 years and several more have occurred nearby in Washington and southern Alaska. Vancouver Island experienced 2 large earthquakes (M > 7.0) in 1918 and 1946 and two more occurred on the mainland in northwest Washington in 1872 and 1949. The largest earthquake in Canada (M = 8.1) occurred near the Queen Charlotte Islands in 1949. The 1946 earthquake near Courtenay was the most destructive in western Canada. Although damaging, these earthquakes all occurred prior to extensive urban development. A smaller earthquake in 1965 near Seattle caused $12 million in damage. The estimated potential economic impact of a similar (M = 6.5) earthquake on the Lower Mainland alone is $14.3 to $32.1 Billion (Munich Reinsurance Company of Canada, 1992: A Study of the Economic Impact of a Severe Earthquake in the Lower Mainland of British Columbia.).

Seismic microzonation maps, also referred to as earthquake hazard maps, are essential tools for effective earthquake emergency and related land use planning. Seismic microzonation maps are detailed (e.g. 1 cm = 200 m) maps that identify the relative potential for ground disruption during an earthquake in different areas. They may include one or more earthquake hazards (liquefaction, amplification, land sliding, tsunamis, subsidence). They are compiled from geologic and geotechnical data and they reflect local ground conditions.

This report was initiated as a step towards advancing the utilization of these maps for planning and resource management purposes in British Columbia as they are extensively used in other seismically active jurisdictions in the Pacific Northwest, such as Washington, Oregon and northern California. They are employed by emergency planners to identify critical facilities that are geologically the most vulnerable including lifeline systems, transportation corridors and emergency centres such as fire halls or medical facilities. For urban planners they are useful for identifying prospective sites for new essential facilities (e.g. schools, hospitals, fire halls, bridges, transportation and utility corridors, toxic waste containment facilities, etc.) or to identify areas requiring special study before development. They may also be used to aid in setting priorities for seismic upgrading or remediation work on existing facilities.

This report addresses the application of knowledge regarding seismic microzonation mapping and assessment in the context of integrated land use planning in British Columbia. The prime objective of the report is to review methodologies currently available for seismic microzonation assessment and mapping and comment on the method(s) considered most suited to user needs in B.C. In this context, seismic microzonation is defined as "the process of determining absolute or relative seismic hazard at many sites accounting for the effects of geologic and topographic amplification of motion and of soil stability and liquefaction, for the purpose of delineating seismic micro zones" (Earthquake Spectra, Vol. 1, No. 1). The report includes a brief analysis of the relative importance of earthquake hazards in the province including ground shaking and amplification of ground shaking, liquefaction (including lateral spreads, flow slides) and seismically induced mass movements (including landslides, debris flows, slumps and rock falls). Emphasis is placed on methods for mapping two of the most important earthquake hazards in the province: liquefaction and amplification of ground motion. Minimum data requirements for these methods are summarized. The report also estimates costs and assesses benefits that would accrue with the adoption of the preferred methodologies, based primarily on data provided by agencies which have completed seismic microzonation mapping studies or which have such work in progress. This includes an assessment of probable benefits to government (local, provincial and federal) and other user groups and a relative judgment of potential cost savings and efficiencies arising from availability of seismic microzonation maps for the province.

Vic Levson, Chair, Seismic Microzonation Task Group, Resource Inventory Committee
Paul Matysek, Chair, Earth Sciences Task Force, Resource Inventory Committee

Ministry of Energy, Mines and Petroleum Resources, Geological Survey Branch, Victoria

EXECUTIVE SUMMARY

Seismic microzonation involves mapping of earthquake-related geologic hazards that depend on site-specific conditions such as soil and groundwater, topography, elevation, and proximity to bodies of water. The first part of this report presents an overview of seismic hazards in British Columbia and examples of mapping techniques considered to represent the state of the practice for three selected hazards (liquefaction, landsliding and amplification of ground shaking). Also presented are examples of the costs and benefits of seismic microzonation work, the costs of selected seismic vulnerability studies and upgrading programs, and discussion of the economic impact of a major earthquake. The second part of the report presents an overview of seismic hazard map preparation issues and general procedures for mapping two of the seismic hazards discussed in Part I: liquefaction and amplification of ground motion.

Seismic hazards can be grouped into six categories for mapping purposes: liquefaction and related phenomena; landslides; amplification of ground motion; tsunamis and seiches; ground rupture; and tectonic subsidence or uplift. A review of published damage reports from selected major historic earthquakes in western North America indicates that liquefaction and landsliding have a relatively high potential for causing damage in British Columbia, followed by ground motion amplification, and tsunamis or seiches in selected areas.

Liquefaction hazard maps are available for numerous parts of the United States and other countries, especially Japan, as well as two Canadian communities: Quebec City and Greater Vancouver. The state of the practice in liquefaction hazard mapping is considered to be represented by the work of Youd and Jones (in press), who assessed the liquefaction susceptibility of the Portland Oregon Quadrangle (1:24 000 scale) and estimated the magnitude of liquefaction-induced lateral ground displacements using an empirical model developed by Bartlett and Youd (1992), which is based on historical lateral displacement data.

Fewer hazard maps are currently available for seismically-induced landslides than for liquefaction, likely due to the greater complexity of landsliding, which can occur in a much greater variety of geologic and topographic settings and with a variety of failure mechanisms. Much of the recent work on earthquake-related landslides has been done at the United States Geological Survey by Keefer and others. A landslide hazard map which is considered to represent the state of the practice is that by Wieczorek et al. (1985), who assessed the relative seismic stability of slopes in San Mateo County, just south of San Francisco, California (1:62 500 scale), using in part an analysis method developed by Newmark (1965).

Hazard maps for ground motion amplification are also relatively uncommon in the literature, although understanding of and interest in this phenomenon has certainly increased in recent years, especially since the Mexico City earthquake of 1985 in which amplification had considerable impact on damage distribution and severity. The state of the practice in ground motion amplification mapping is considered to be represented by the work of Elton and Martin in Charleston, South Carolina (1989), who used the computer program SHAKE (Schnabel et al, 1972) to predict the distribution of dynamic site period across the city.

The potential economic impact of a major earthquake on the Lower Mainland, estimated to be $14.3 to $32.1 billion (Munich Reinsurance, 1992), has been extrapolated in this report to represent on the order of $22 billion to $49 billion for the whole province. Properly implemented, seismic microzonation is one tool for mitigating the severity of that economic impact. Seismic microzonation costs are shown to be generally small compared to the economic impact of a major earthquake and to the costs of seismic vulnerability studies and upgrading programs currently underway or proposed by various public sector agencies in British Columbia.

TABLE OF CONTENTS

SUMMARY

PART I - BACKGROUND

1. INTRODUCTION

1.1 General

1.2 Seismic Hazard Mapping Applications

2. SEISMIC HAZARDS IN BRITISH COLUMBIA

2.1 Seismic Hazard Terminology and Types

2.2 Seismic Hazards From Historic Western North American Earthquakes

2.3 Relative Importance of Liquefaction and Landsliding Across the Province

2.4 General Ranking of Seismic Hazards in British Columbia

2.5 Study Focus

3. LIQUEFACTION

3.1 General

3.2 State of the Practice in the Western United States

3.2.1 General

3.2.2 Methodology

3.2.3 Data Requirements

3.3 Mapping in Canada

4. LANDSLIDES

4.1 General

4.2 State of the Practice in the Western United States

4.2.1 General

4.2.2 Methodology

4.2.3 Data Requirements

4.3 Mapping in Canada

5. AMPLIFICATION OF GROUND MOTION

5.1 General

5.2 Mapping Parameters

5.3 Survey of Ground Motion Amplification Maps

5.4 State of the Practice in the United States

5.5 Mapping in Canada

5.5.1 Quebec City, Quebec

5.5.2 Victoria, British Columbia

6. INTEGRATED HAZARD MAPS

7. COST/BENEFIT INFORMATION

7.1 General

7.2 Economic Impact of Earthquakes

7.3 Costs of Seismic Work

7.3.1 General

7.3.2 Seismic Vulnerability Studies and Upgrading Programs

7.3.3 Lower Mainland Liquefaction Hazard Maps 56

7.3.4 Comparative Assessment of Seismic Risks of Various Native Communities

7.3.5 Portland Oregon Relative Seismic Hazard Mapping

7.3.6 National Earthquake Hazards Reduction Program

7.3.7 Data Availability in British Columbia

7.4 Benefits of Seismic Hazard Mapping

PART II - MAP PREPARATION GUIDELINES

8. INTRODUCTION

8.1 General

8.2 Map Format

8.3 Map Scale, Precision and Accuracy

8.4 Geographic Information Systems

9. LIQUEFACTION

9.1 General

9.2 Level I Map

9.2.1 General

9.2.2 Ground Information Requirements

9.2.3 Mapping Parameters and Procedures

9.3 Level II Map

9.3.1 General

9.3.2 Ground Information Requirements

9.3.3 Mapping Parameters and Procedures

9.4 Level III Map

9.4.1 General

9.4.2 Ground Information Requirements

9.4.3 Mapping Parameters and Procedures

10. AMPLIFICATION OF GROUND MOTION

10.1 General

10.2 Level I Map

10.2.1 General

10.2.2 Ground Information Requirements

10.2.3 Soil Susceptibility Categories

10.2.4 Mapping Procedures

10.3 Level II Map

10.3.1 General

10.3.2 Ground Information Requirements

10.3.3 Mapping Parameters and Procedures

10.4 Level III Map

10.4.1 General

10.4.2 Ground Information Requirements

10.4.3 SHAKE Analysis Procedures

10.4.4 Mapping Parameters and Procedures

REFERENCES

TABLES

TABLE 1 - NATIONAL BUILDING CODE OF CANADA SEISMIC ZONES

TABLE 2 - SELECTED MAJOR EARTHQUAKES IN WESTERN NORTH AMERICA

TABLE 3 - LIQUEFACTION HAZARD MAPS

TABLE 4 - GEOLOGIC ENVIRONMENTS LIKELY TO PRODUCE EARTHQUAKE-INDUCED LANDSLIDES IN THE LOS ANGELES REGION

TABLE 5 - NATIONAL BUILDING CODE OF CANADA FOUNDATION FACTORS

TABLE 6 - GROUND MOTION AMPLIFICATION MAPS

TABLE 7 - ECONOMIC IMPACT OF EARTHQUAKES ACROSS BRITISH COLUMBIA

TABLE 8 - SURFICIAL GEOLOGY AND RELATED MAPPING COVERAGE OF BRITISH COLUMBIA

TABLE 9 - ESTIMATED SUSCEPTIBILITY OF SEDIMENTARY DEPOSITS TO LIQUEFACTION DURING STRONG SEISMIC SHAKING

TABLE 10 - ESTIMATED SUSCEPTIBILITY TO LIQUEFACTION OF LOWER MAINLAND SOILS

TABLE 11 - CATEGORIES FOR SOIL SUSCEPTIBILITY TO AMPLIFICATION

TABLE 12 - AMPLIFICATION FACTORS

FIGURES

FIGURE 5.1 - APPROXIMATE RELATIONSHIPS BETWEEN MAXIMUM ACCELERATIONS ON ROCK AND OTHER SITE CONDITIONS

FIGURE 5.2 - VARIATIONS OF ACCELERATIONS ON SOFT SOIL SITES VS ROCK SITES

APPENDICES

APPENDIX I - CONTRACT SCHEDULE A - SERVICES AND CONTACTS

APPENDIX II - RESOURCE INVENTORY COMMITTEE TASK FORCE - GUIDELINES FOR DATA MODELS

APPENDIX III - EXAMPLE SEISMIC HAZARD MAPS

DRAWINGS

DRAWING A-2001 - MAXIMUM PROBABILITY OF LIQUEFACTION IN BRITISH COLUMBIA

DRAWING A-2002 - MAXIMUM PROBABILITY OF SEISMICALLY INDUCED ROCK FALLS IN BRITISH COLUMBIA

DRAWING A-2003 - PEAK GROUND ACCELERATIONS FOR ONE THOUSAND YEAR GROUND MOTIONS

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