Cycle 1 (2011 Deadline)
Earthquake-generated landslide hazard in Lebanon
PI: Grace Abou-Jaoude, Lebanese American University
U.S. Partner: Joseph Wartman, University of Washington
Project Dates: May 2012 - April 2014
Lebanon is located in a relatively high seismic zone and has a rugged topography, making it vulnerable to hazards from earthquakes and landslides. Records about seismic events in the country go back to 303 AD and contain descriptions about such damages as houses and monuments destroyed and widespread fires, but they offer few if any details about collateral damages from landslide hazards associated with earthquakes. Although Lebanon has not experienced any major earthquake since 1956, the recent discovery of an active thrusting fault close to its coastline has significantly raised its risk of being hit by a high magnitude earthquake. Past studies on seismic hazards in Lebanon have focused on seismic zoning and its impact on structural engineering design. Although many researchers have assessed slope stability hazards in Lebanon based on various static conditions, no effort has been undertaken as yet to assess the impact of a seismic event on triggering landslide hazards in the country.
This project aims to produce a hazard map of Lebanon that clearly shows the critical areas prone to earthquake-induced landslides. This goal will be achieved through three major activities to be conducted over a period of two years. The first task will be mapping the landslide prone zones in the Geographic Information Systems (GIS) framework, followed by a detailed geological field survey. The second task will focus on numerical modeling of slopes, including seismic slope stability analyses in order to evaluate the failure potential of sloping terrains when subjected to different seismic loading events. The third task will be to produce an up-to-date earthquake-induced landslide hazard map, taking into consideration the effects of the active faults in the country, the general terrain parameters, and the seismic slope stability analyses. Ultimately the project should help Lebanese cities to identify areas with high natural hazard potential so they can plan urban growth appropriately, thus preventing damage to critical infrastructure and saving lives in the event natural disasters strike.
Summary of Recent Activities
During the last reporting period, Dr. Abou-Jaoude’s research team conducted a parametric study using the RocScience SLIDE software to obtain the horizontal seismic yield coefficient ky for different slope angles and soil strength parameters. Strength parameters were estimated based on the input received from the geologist and based on the samples retrieved from the field visit during the last quarter. The thresholds for disrupted (D) and coherent (C) modes of failure were set based on slope angle. An extensive literature review was completed and two failure criteria were used to model these modes of failure on SLIDE. Two pseudo-static limit equilibrium methods were used during the analysis: Spencer (1967) method and Simplified Bishop (1955) method with circular slip surfaces and allowing tensile normal forces to develop at the base of the slope. Over 1000 iterations were performed using the Mohr-Coulomb failure criteria and over 1200 iterations were performed using the Hoek-Brown failure criteria, and iterations are still ongoing. The preliminary results from the models were used to generate slope stability charts. The iterations on SLIDE are ongoing as refinements are made after the preliminary results are checked and interpreted. The final stability charts will be used to update the analysis on ArcGIS and compare the results with the previously performed analysis based on Newmark’s infinite sliding block method. Probability of failure will be calculated for all slopes and a risk map will be generated for earthquake-induced landslides in Lebanon. The results obtained during the first year of the project are expected to be published. Collaboration during the reporting period was also ongoing and a couple of meetings were held with the U.S. partner during the past quarter. During January-March 2014, the team is expecting to generate a new model on ArcGIS that considers the modes of failure, thresholds, and newly derived stability charts. Displacement/factor of safety for lateral spreading (LS), disrupted (D), and coherent (C) landslide categories will be computed for the regional map as well. A workshop is planned to take place May 2014 to disseminate the results of the project and set future direction of studies on earthquake-induced landslides in Lebanon and the region.