Seismotectonics of Mongolia and Baikal Rift Zone Controlled by Lithospheric Structures
Zhouchuan Huang, Dapeng Zhao
Abstract
Abstract Active tectonics are developing in Mongolia and the Baikal rift zone, where large crustal earthquakes (Mw ≥ 6.0) occur frequently. To clarify the mechanism of these earthquakes, we determine a high‐resolution 3‐D P ‐wave velocity model of the crust and upper mantle beneath Mongolia and the Baikal rift zone. We find an annular high‐velocity zone in the lithosphere; whereas low‐velocity anomalies exist both inside and around the high‐velocity ring as well as beneath the rift zone. Strong interactions between the high‐velocity ring and the surrounding terranes may have induced many moderate‐to‐large earthquakes (Mw 5–7). By contrast, mega‐earthquakes (Mw ≥ 8.0) occurred right above the high‐velocity ring. We propose that the high‐velocity ring is strong as a whole; it sustains the stress arising from the India‐Asia collision and causes the mega‐earthquakes. Meanwhile, the ring could protect the Hangay Dome from the regional compression, leading to weak seismicity under the dome.