EARTHQUAKE-INDUCED LANDSLIDES 25 YEARS LATER David Keefer

CHRONOLOGICAL OUTLINE BEFORE 25 YEARS AGO Before 1783 1783 through 1947 1948 through 1983 THE LAST 25 YEARS

TOPICAL OUTLINE Post-earthquake investigations and inventories Worldwide and regional-scale synthesis of data Hazard mapping and evaluation Geomorphology and landscape evolution Paleoseismology NOTE: NOT discussing site-specific seismic slope-stability analyses, laboratory testing of materials, etc.

ANCIENT TIMES (BEFORE 1783) Landslides mentioned as earthquake effects as early as 1789 BCE in China (Hansen and Franks, 1991), BUT Data for any given earthquake are very incomplete Descriptions of locations and characteristics are vague Earthquakes are pre-instrumental, so epicenters, etc. poorly constrained At worst, “data” are misleading

1783-1947: GROUND-BASED SCIENTIFIC POST-EARTHQUAKE INVESTIGATIONS Characteristics Ground-based surveys of large areas Landslides documented along with other earthquake effects Large (but not necessarily complete) sampling of landslide localities More precise and detailed descriptions of characteristics than before this time Notable Examples 1783 Calabria, Italy (M 7) (Sarconi, 1784; Lyell, 1874) 1811-1812 New Madrid, Missouri USA M 7.3-7.8 (Fuller, 1912) 1886 Charleston, South Carolina, USA (M 6.8) (Dutton, 1989) 1897 Assam, India (M 8.3) (Oldham, 1899) 1906 San Francisco, California, USA (M 7.8) (Lawson, 1908) 1934 Bihar, India-Nepal (M 8.1) (Geological Survey of India, 1939)

1948 THROUGH 1983 Use of aerial photography to map landslides Extensive to “complete” landslide inventories with detailed data on locations and characteristics

COMPLETE LANDSLIDE INVENTORIES THROUGH 1983 EARTHQUAKE DATE M NUMBER OF LANDSLIDES REFERENCES Daly City, Calif. USA 22-May-1957 5.3 23 Bonilla, 1960 Guatemala 4-Feb-1976 7.5 ~50,000 Harp et al., 1981 Mt. Diablo, Calif. USA 24-Jan-1980 5.8 103 Wilson et al., 1985 Mammoth Lakes, Calif. USA 25-May-1980 6.2 5253 Harp et al.,1984 Coalinga, Calif. USA 2-May-1983 6.5 9389 Harp and Keefer, 1990

1964 ALASKA M 9.2 (> 60 reports) Area too large (269,000 km2) and much of it too remote for complete inventory “Thousands of landslides,” at least Nevertheless, much detailed information on landslides in numerous reports Landslides caused 56% of economic loss and at least 45 of the 130 deaths Detailed site-specific analyses of large landslides in Anchorage, Alaska’s largest city Turnagain Heights Landslides, Anchorage

1970 PERU M 7.9 (Cluff, 1971; Plafker et al., 1971) First extensive airphoto inventory for large earthquake Large landslides mapped throughout central area of 8300 km2 Nevados Huascarán rock avalanche killed >25,000 people (From Plafker et al., 1971)

OTHER NOTABLE POST-EARTHQUAKE INVESTIGATIONS: 1948-1983 1959 Hebgen Lake, Mont. USA M 7.1 (Hadley, 1964) 1971 San Fernando, Calif. USA M 6.7 (Morton, 1971, 1975) 1976 Friuli, Italy M 6.3-6.5 (Govi, 1977, Govi and Sorzana, 1977) 1978 Izu-Oshima Kinkai, Japan (Geographical Survey Institute of Japan, 1978; Okusa and Anma, 1980) 1980 Irpinia, Italy M 6.9 (Agnesi et al. 1983; Carrera et al., 1986; Del Gaudio et al. 2000; Wasowski et al., 2002; Del Gaudio and Wasowski, 2004)

NEWMARK SEISMIC SLOPE STABILITY ANALYSIS HAZARD EVALUATION NEWMARK SEISMIC SLOPE STABILITY ANALYSIS Developed by Newmark (1965) Field verified by Wilson and Keefer (1983) Applied on regional scale by Wieczorek et al. (1985) (From Wilson and Keefer, 1983; Jibson et al. 2000)

1948 THROUGH 1983 Post-earthquake investigations and inventories Worldwide and regional-scale synthesis of data First worldwide compilation (for liquefaction-induced landslides; Seed, 1967 Terzaghi Lecture) First regional compilation (for northern California, including 1906 San Francisco earthquake; Youd and Hoose, 1978) Hazard mapping and evaluation Geomorphology and landscape evolution First landscape evolution study (for Southern Alps, New Zealand; Adams, 1980) Paleoseismology Simonett, 1967--pioneered statistical method, using 1935 New Guinea earthquake (M 7.9)

25 YEARS AGO (1984): First general synthesis of worldwide data

25 YEARS AGO: ANALYSIS OF WORLDWIDE DATASET (Keefer, 1984) Sample of 40 worldwide earthquakes M > 5.2 (Supplemented several hundred small US events to determine minimum M for triggering) Classification Abundance DISRUPTED SLIDES AND FALLS Rock falls Soil falls Rock slides Disrupted soil slides Rock avalanches Soil avalanches COHERENT SLIDES Rock slumps Soil slumps Rock block slides Soil block slides Slow earth flows LATERAL SPREADS AND FLOWS Soil lateral spreads Rapid soil flows Subaqueous landslides

DISRUPTED SLIDES AND FALLS Highly disrupted masses (small blocks, fragments, or particles) Steep slopes (may run out onto gentle slopes) High velocity Move long distances Shallow (< 3 m deep), except for rock avalanches Moderate to high casualty potential for rock (low for soil) Low to moderate historical damage costs Soil falls Rock falls Disrupted soil slides Rock slides Soil avalanches Rock avalanches

COHERENT SLIDES Relatively coherent masses (one or a few large blocks) Moderate slopes Low velocity Move short distances Deep (> 3 m) Low to moderate casualty potential (higher for soil) Moderate to high historical damage costs Soil slumps Rock slumps Soil block slides Rock block slides Slow earth flows

LATERAL SPREADS AND FLOWS Mostly liquefied mass (soil flow) Blocks moving on subsurface liquefied zone (lateral spread) Gentle slopes to level ground High velocity Move long distances (soil flows) High casualty potential for soil flows High historical damage costs for lateral spreads Soil lateral spreads Rapid soil flows Subaqueous landslides

EARTHQUAKE MAGNITUDE VS. AREA AFFECTED BY LANDSLIDES

Disrupted Coherent Disrupted Coherent MAGNITUDE VS. MAXIMUM EPICENTRAL DISTANCE MINIMUM MODIFIED MERCALLI INTENSITY Disrupted Coherent Disrupted Coherent Lateral Spreads and Flows Upper Bounds Lateral Spreads and Flows

THE LAST 25 YEARS: 1984-Present Improvements in remote sensing Use of Geographic Information Systems (GIS)

COMPLETE LANDSLIDE INVENTORIES, 1984-PRESENT

1999 CHI-CHI, TAIWAN M 7.5 Most extensive landslide studies of any earthquake ever. Many, many studies and publications covering virtually all aspects of earthquake-induced landslides. 26,000 landslides mapped from aerial photographs (Wang et al., 2002); 9272 large landslides mapped from SPOT satellite images (first use) (Liao and Lee, 2000) > 400 free-field strong motion recordings for correlation

LOMA PRIETA, CALIF. EARTHQUAKE M 6. 9 Landslide Concentration vs LOMA PRIETA, CALIF. EARTHQUAKE M 6.9 Landslide Concentration vs. Slope and Material (From Keefer, 2000)

LANDSLIDE CONCENTRATION VS. DISTANCE LOMA PRIETA, CALIF. EARTHQUAKE M 6.9 (From Keefer, 2000)

WORLDWIDE AND REGIONAL ANALYSES SINCE 1984 Worldwide (Rodríguez et al., 1999) Landslide Damage (Bird and Bommer, 2004) New Zealand (Hancox et al., 1997, 2002) Italy (Prestininzi and Romeo, 2000) Greece (Papadopoulos and Plessa, 2000) Central America (Bommer and Rodríguez, 2002)

MAGNITUDE VS. AREA AFFECTED BY LANDSLIDES (Rodríguez et al., 1999) Keefer, 1984

MINIMUM INTENSITIES FOR LANDSLIDES (Rodríguez et al., 1999) Number of earthquakes

Northridge, California area (from Jibson et al., 2000). REGIONAL-SCALE EVALUATION OF SEISMIC SLOPE STABILITY USING NEWMARK METHOD Northridge, California area (from Jibson et al., 2000). (Area is ~2.5x4 km)

TIME-PROBABILISTIC EVALUATION OF EARTHQUAKE-INDUCED LANDSLIDE HAZARD (Del Gaudio et al., 2000, 2003; Romeo, 2000) (From Del Gaudio et al., 2003) (From Romeo, 2000)

HAZARD ANALYSES USING STATISTICAL METHODS Probability of earthquake-induced slope failure, upper Serchio River basin, Italy (Luzi et al., 2000) Probability of earthquake-induced slope failure, Kouhsing Quadrangle, Taiwan (Lee et al., 2008)

HAZARD ANALYSIS USING COMPUTING WITH WORDS, OR “FUZZY LOGIC” “Comprehensive Areal Model of Earthquake-Induced Landslides (CAMEL) ( Miles, 2004; Miles and Keefer 2007, 2008, 2009) “Possibility Module” “Intensifier Module”, Probability Determination

SAMPLE RESULTS FROM CAMEL APPLIED TO 1906 SAN FRANCISCO EARTHQUAKE, SANTA ROSA AREA, CALIFORNIA (Swank, 2007) Rock falls Soil slumps

Divide by Area to Calculate Erosion Rate Seismic Moment vs. Total Volume of Landslide Material Combine with Earthquake History to get Rate of Seismic Moment Release GEOMORPHOLOGY: CALCULATING EROSION RATES FROM EARTHQUAKE-INDUCED LANDSLIDES (Keefer, 1994) Calculate Total Volume of Landslide Material Produced Over Time Divide by Area to Calculate Erosion Rate

REGIONAL EROSION RATES FROM EARTHQUAKE-INDUCED LANDSLIDES

MODELING EROSION RATE FROM EARTHQUAKE-INDUCED LANDSLIDES (Malamud et al., 2004)

GEOMORPHOLOGY AND LANDSCAPE EVOLUTION: TWO TYPES OF STUDIES Post-earthquake sediment transport, Chi-Chi, Taiwan (Dadson et al., 2004) Distribution of landslides related to topography and earthquake source: Chi-Chi, Finisterre, and Northridge earthquakes (Meurnier et al., 2007)

PALEOSEISMOLOGY-ROTATIONAL SLUMP IN PYRAMID AT CARAL, PERU From Sandweiss et al., 2009 For comprehensive discussion of using landslides as paleoseismic indicators, see Jibson, 1996 Evidence of contemporaneous repairs, so dates to ~2000 BCE Dry (hyperarid) conditions, and no likely cause other than earthquake Distribution and severity of this and other earthquake effects suggests M>7.8

SO... IN THE LAST 25 YEARS MUCH HAS BEEN ACCOMPLISHED TO INCREASE OUR UNDERSTANDING OF EARTHQUAKE-INDUCED LANDSLIDES This includes advances in the areas I’ve talked about, as well as advances in areas(such as site-specific seismic slope-stability analysis) that I haven’t talked about. Much of the current state of knowledge will be presented in the papers at this Conference during the next 4 days HOWEVER...

WE CURRENTLY HAVE ONLY 18 (+/-) “COMPLETE” INVENTORIES WORLDWIDE 13 of those inventories were produced in the last 25 years During this time, according to the US Geological Survey, there were: 450 earthquakes of M > 7, 3800 earthquakes of M > 6, and 36,775 earthquakes of M > 5 Comprehensive inventories are important because they provide the basic data for all other studies, Only with complete inventories can we differentiate between types of slopes that failed and types of slopes that didn’t Large number of variables involved in earthquake-induced slope failure means that a large dataset is necessary for statistically-significant analysis

THE GREATEST RESEARCH NEED I SEE IS FOR COMPLETE INVENTORYING AND COMPREHENSIVE STUDY OF LANDSLIDES GENERATED BY MANY MORE EARTHQUAKES IN THE FUTURE.