Improving the level of seismic hazard parameters in Saudi Arabia using earthquake location

Abstract

Saudi Arabia is characterized as largely aseismic; however, the tectonic plate boundaries that surround it are very active. To improve characterization of seismicity and ground motion hazard, the Saudi Arabian Digital Seismic Network (SANDSN) was installed in 1998 and continues to be operated by the Saudi Geological Survey (SGS) and King Abdulaziz City for Science and Technology (KACST). This article describes research performed to improve seismic hazard parameters using earthquake location and magnitude calibration of the high-quality SANDSN data. The SANDSN consists of 38 seismic stations, 27 broadband, and 11 short period. All data are telemetered in real time to a central facility at KACST in Riyadh. The SANDSN stations show low background noise levels and have good signal detection capabilities; however, some stations show cultural noise at frequencies above 1.0 Hz. We assessed the SANDSN event location capabilities by comparing KACST locations with well-determined locations derived from ground truth or global observations. While a clear location bias exists when using the global average iasp91 earth model, the locations can be improved by using regional models optimized for different tectonic source regions. The article presents detailed analysis of some events and Dead Sea explosions where we found gross errors in estimated locations. New velocity models we calculated that should improve estimated locations of regional events in three specific regions include (1) Gulf of Aqabah—Dead Sea region, (2) Arabian Shield, and (3) Arabian Platform. Recently, these models were applied to the SANDSN to improve local and teleseismic event locations and to develop an accurate magnitude scale for Saudi Arabia. The Zagros Thrust presents the most seismic hazard to eastern Saudi Arabia because of the frequent occurrence of earthquakes. Although these events are 200 km or further from the Arabian coast, wave propagation through sedimentary structure of the Gulf causes long-duration ground motions for periods between 3 and 10 s. Such ground motions could excite response in large engineered structures (e.g., tall buildings and long bridges) such as was experienced after the November 22, 2005 Qeshm Island earthquake off the southern coast of Iran.