HR: 17:00h
AN: H44A-05    [Abstracts]
TI: Earthquake Induced Landslides in the Old City of Zefat, N Israel; History, Current Hazard and the Influence of 2000 Years of Human Habitation
AU: * Katz, O
EM: odedk@mail.gsi.gov.il
AF: Geological Survey of Israel, 30 Malkhei Israel St., Jerusalem, 95501 Israel
AU: Crouvi, O
EM: crouvi@mail.gsi.gov.il
AF: Geological Survey of Israel, 30 Malkhei Israel St., Jerusalem, 95501 Israel
AB: The old quarter in the city of Zefat (Northern Israel) has a long history of repeated damage from earthquakes, probably due to earthquake-induced landslides (EILS). In this study we examine field and historical evidence for static and dynamic slope instability in Zefat and evaluate the current EILS hazard in light of its long (ca. 2000 years) human habitation that profoundly changed the natural geotechnical conditions. The city of Zefat is located on the slope of an elevated region bordering the seismogenic Dead Sea transform. The bedrocks are mainly marls, chalks and limestones of Santonian to Eocene times, but most of the city is built on more than 10 meters of anthropogenic talus/strata of two types: (1) talus-like: inclined ($>$$30\deg$) layers of pebbles and pottery embedded in unconsolidated earth fill and (2) ruins filled and covered by earth. Meter-scale slumps and mudflows are common in this material during the rainy season. We evaluate the EILS hazard with GIS based Newmark analysis using as base layers D.T.M with 625m-sq grid cell size and a geotechnical map. Each exposed geotechnical unit was assigned mechanical properties (cohesion, angle of internal friction, density) reflecting its lithology and slope stability properties. For calibration of the assigned mechanical model, we first analyzed the M=6, October 1759 and M=7, January 1837 earthquakes, both with distance to fault rapture zone (R) of about 15km. Sites of slope failure in these earthquakes were mapped using field evidence and historical chronicles of damaged synagogues. The M=5 earthquake of August 1984 (R=50km) with no EILS was also analyzed. Calibration was satisfied when calculated slope failure was comparable to the mapped historical reports and field observations of slope instability. To evaluate the current hazard, 20 theoretical earthquakes in the magnitude range of 4-7 and epicentral distances of 10-120km were analyzed, using the calibration described above. We found that M=7, M=6 and M=5 earthquakes will induce landslides in Zefat in R of more than100km, 50km and 10km respectively. Most slope failure will occur in the anthropogenic talus. Structures and lifelines founded in the talus will probably be heavily damaged. Anthropogenic talus is common in Near-East cities with long habitation history. Understanding its seismic behavior will reduce damage in future earthquakes.
DE: 7223 Seismic hazard assessment and prediction
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting