Stress Transfer Along the Western Boundary of the Bayan Har Block on the Tibet Plateau From the 2008 to 2020 Yutian Earthquake Sequence in China

• Published in: Geophysical research letters 2021-08, Vol.48 (15), p.n/a
• Main Authors: Jia, Ke, Zhou, Shiyong, Zhuang, Jiancang, Jiang, Changsheng
• Format: Article
• Language: English
• Subjects: background seismicity change; Bayan Har block; Coulomb stress change; ETAS model
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL094125

Eight Ml ≥ 7.0 earthquakes have occurred around the Bayan Har block, NW Tibet, China, since 2000, resulting in a large number of casualties. Near the western boundary of the Bayan Har block, four Ml ≥ 6.0 Yutian earthquakes have occurred from 2008 to 2020. Stress interactions among them are comprehensively investigated by applying the ETAS (Epidemic‐Type Aftershock Sequence) model and calculating ΔCFS (Coulomb failure stress change) from a 3D linear viscoelastic mode. The combined (coseismic plus postseismic) ΔCFS induced by proceeding Yutian earthquakes on hypocenters of the 2012, 2014, and 2020 Yutian earthquakes are −1.5 × 10−4, 3.6 × 10−3, and 1.5 × 10−1 MPa, respectively. The background probabilities of the 2008, 2012, 2014, and 2020 Yutian earthquakes are 0.87, 0.97, 1.5 × 10−3, and 8.7 × 10−5, respectively. Combining those two independent approaches, we conclude that the 2008 and 2012 Yutian earthquakes are more like background earthquakes and that the 2014 and 2020 Yutian earthquakes were triggered by the proceeding Yutian earthquakes. Plain Language Summary Along the boundaries of the Bayan Har block, NW Tibet, China, there have been eight large earthquakes since 2000, resulting in a large number of casualties and countless economic losses. At its western boundary (Yutian region), four earthquakes with local magnitudes larger than 6.0 have occurred since 2008. Whether these four large earthquakes were triggered is an important question to assess regional seismic hazards. We combine two methods to address this issue. One is the direct calculation of stress transfer and the other is the estimation of the probabilities of them being background events (an event is driven by tectonic loading). We find that the stress transfer from proceeding major earthquakes to the 2012 Yutian earthquake is smaller than the earthquake triggering threshold (0.01 MPa), while those of the 2014 and 2020 Yutian earthquakes were comparable with the triggering threshold. The background probabilities of the 2008 and 2012 Yutian earthquakes are high (close to 1.0), while the background probabilities of the 2014 and 2020 Yutian earthquakes are very low (close to 0.0). Thus, we conclude that the 2008 and 2012 Yutian earthquakes are more like background earthquakes and that the 2014 and 2020 Yutian earthquakes were triggered by the proceeding Yutian earthquakes. Key Points Four Ml ≥ 6.0 have occurred on the western boundary of the Bayan Har block, NW Tibet, China, from 2008 to 20