The 4th International IASPEI/IAEE Symposium on the Effects of Surface Geology on Seismic Motion (ESG4) was held at the University of California Santa Barbara from August 23 - 26, 2011. The first three Symposia were held in 1992 in Odawara, Japan, in 1998 in Yokohama, Japan, and in 2006 in Grenoble, France. The ESG working group was created jointly by IASPE (International Association of Seismology and Physics of the Earth's Interior) and IAEE (International Association of Earthquake Engineering) almost thirty years ago to promote a greater understanding and analysis of the effects of surface geology on ground motion.
The effects of local site conditions on earthquake ground motions can be documented as early as the 1906 San Francisco earthquake, where soft soils near the ground surface amplified the incoming accelerations. In the more recent era, many events have caused destruction hundreds of miles from the causative fault due to local site effects. Cities located in alluvial basins, such as Los Angeles, Tokyo, and Osaka, can experience significant damage from earthquake waves that are reflected at the edges of the basin. Other major site effects are caused by material non-linearity and topography. Topography is a source of signal amplification and deamplification that causes spatial variation of ground motions. The most familiar and devastating nonlinear response is liquefaction, which was dramatically observed in 2011 in Christchurch (M6.3, 22 February 2011) and Japan (M9.0, 11 March 2011).
The Symposium at UCSB consisted of a pre-meeting NEES workshop,16 plenary sessions, and a half-day workshop on the Vs30 debate. The invited speakers were an international group of scientists and engineers who spoke on diverse topics from the state of the art of ground motion research and practice. Papers submitted to the Symposium were presented in poster sessions each day.
Professor Ralph Archuleta of the Department of Earth Science at UCSB is the Chairman of the Symposium. Professor Archuleta is a seismologist with expertise in the analysis and prediction of strong ground motions from earthquakes.