EARTHQUAKE FAULTS OF CENTRAL MONGOLIA: IMPLICATIONS FOR THE SEISMIC SAFETY OF ULAANBAATAR

Four earthquakes have been recorded in Mongolia since 1906 in the range of M7.4 to M8.1. These earthquakes occurred along strike-slip faults in sparsely populated regions and caused little damage to Ulaanbaatar, the capitol of Mongolia. About 35% of Mongolia’s three million people live in the Ulaanbaatar. Many live in multi-story, soviet-style apartment buildings. Seismic hazard assessment, including the identification of potentially active faults, is critically important to the population and economic stability of this city.

The neotectonic architecture of Mongolia is delineated by sets of faults that accommodate the Tertiary and Quaternary shortening of this part of central Asia. Seismicity in Mongolia over the past 100 years is puzzling because the low rates of crustal movement unexpectedly produce large magnitude earthquakes. Two of the largest historic earthquakes occurred on the well studied Bulnay and Bogd strike-slip faults. However, there are many other faults capable of generating significant earthquakes and they remain relatively unexplored and potential hazards to the growing population centers of Mongolia. Recent field studies by California State University, Long Beach (CSULB) and the Mongolian University of Science and Technology (MUST) have identified several seismically active faults within 300 km of Ulaanbaatar. These research efforts have used state-of-the-art remote sensing techniques and geological field mapping to characterize the seismic activity and kinematics of poorly understood faults. Four seismically active fault zones have been identified and include the: (1) Deren fault zone, (2) Hustain fault, (3) Buren fault, and (4) Harhorin fault. These fault zones have three distinctive strike directions (NW, NE and E) and exhibit active geomorphic features. A recent earthquake has occurred in the vicinity of the Deren fault zone in January, 2010 (M5.4). There are also at least three more faults in the study area that warrant further investigation.