CRUSTAL STRUCTURE OF KHÖVSGÖL, MONGOLIA

The Khövsgöl rift system is a seismically active area located within the Asian continental interior between the Baikal rift to the northeast, Sayan Mountains to the north, and Altay Mountains to the southwest. This rift system contains three N-S trending parallel basins; Khövsgöl being the deepest and easternmost rift of the Khövsgöl rift system. Like the Baikal rift, the Khövsgöl rifts are structures that accommodate extension where the Siberian craton meets a belt of accreted terranes to the south. Structures inherited during the accretionary events may be a factor that influences regional deformation. The forces driving transtension in this setting are not well known but have been attributed to processes ranging from mantle plume activity, to far-field effects of Indian-Eurasian plate convergence. The primary goal of this work is to better understand the northern Mongolian rift setting by examining and identifying relationships between local seismicity and crustal structures.

The Khövsgöl seismic array was deployed from August 2014 to June 2016 and consisted of 26 broadband seismic stations spread over 200 square kilometers of northern Mongolia. Here we focus on 43 well-recorded events within the array that have local magnitudes greater than 2. Most events were located in the Darhat and Khövsgöl rifts. The largest earthquake recorded was a magnitude ml=5.2 that occurred beneath Lake Khövsgöl on 12-05-2014. Epicenters in the Khövsgöl rift were dispersed throughout the northern portion of the rift, and range in depth from 5 to 20 kilometers. East of Khövsgöl, Darhat rift contained 19 events, 13 of these earthquakes occurred along the eastern border of the valley delineating an active fault along the eastern margin of the rift. Earthquakes along the fault were 5 to 15 kilometers deep while other Darhat events occurred up to 21 kilometers below the surface. Events located outside of the rifts were at the southern termination of the array and ranged from near surface to 20 kilometers depth.