Stress change near the Kunlun fault before and after the Ms 8.1 Kunlun earthquake

Abstract

On 14 November, 2001, a great earthquake of Ms 8.1 occurred on the Kunlun fault in the Kusai Lake segment of the Kunlun Mountain, Qinghai Province in northwest China. The stresses measured at the sites near the Kunlun fault before and after the earthquake show a great drop after the earthquake. The values of the horizontal maximum principal stress at two sites are 12.9 Mpa and 6.8 Mpa before the earthquake. Measurement of the horizontal maximum principal stress at the same sites after the earthquake, showed values of 3.5 Mpa and 2.2 Mpa respectively. This is only about one‐third of that before the earthquake. Apparently stress that accumulated near the fault before the earthquake was released along with the rupturing of the surface. The direction of the maximum horizontal principal stress also varies before and after the earthquake. The direction is found to deviate from that of the regional structure stress field after the earthquake. Such stress changes offer a basis for predicting large earthquakes in the region.

Dynamic simulation of interactions between major earthquakes on the Xianshuihe fault zone

“…The stress drop of major earthquake is mainly less than 10 MPa. For example, the actual stress measurement results show that the crustal stress near the Kunlun fault after the Ms8.1 Kunlun earthquake in 2001 is only about one third of that before the earthquake and the stress drop is between 4.6 and 9.4 MPa [31] . The results derived from digital seismology show that the stress drop of major earthquake is relatively low in Sichuan-Yunnan region [32,33] .…”

The stress state of the Beichuan-Jiangyou segment of the Longmenshan fault before and after the Wenchuan M S 8.0 Earthquake

“…A large earthquake generally has a greater impact on the in situ stress field around the vicinity of the earthquake focal area, which predominantly manifests as a fraction of maximum principal stress or a deflection of its orientation after the earthquake (Liao et al, 2003;Li et al, 1982;Li and Wang., 1979). The Wenchuan M S 8.0 Earthquake ruptured two NW-dipping reverse faults along the Longmenshan fault belt at the eastern margin of the Tibetan Plateau (Li et al, 2009;Chen et al, 2008).…”

Near-surface stress measurements in the Longmenshan fault belt after the 2008 Wenchuan Ms8.0 earthquake

“…Large earthquakes generally have a significant effect on the in situ stress field in the earthquakes focal area and the vicinity, which mainly manifests as a decrease in the maximum principal stress or a deflection of its orientation after the earthquake [2][3][4]. The Wenchuan M s 8.0 earthquake ruptured two NW-dipping reverse faults along the Longmenshan fault belt at the eastern margin of the Qinghai-Tibet Plateau [28,29], and generated a 240 km long surface rupture along the Beichuan-Yinxiu fault (which shows right-lateral oblique faulting), with maximum vertical and horizontal co-seismic displacements of 6.2 and 4.9 m, respectively [30][31][32].…”

“…The magnitude or orientation of the maximum principal stress (near-surface) can change significantly before and after large earthquakes in the earthquake focal area and the surrounding region. For example, Lia et al [2] used the overcoring method to obtain in situ stress measurements (depth (H) o30 m) in the central Qinghai-Tibet Plateau before and after the Kokoxili M s 8.1 earthquake (Nov. 14th, 2001, Qinghai Province, China), and found the variation in the magnitude of the maximum principal stress. Their measurements showed that the maximum principal stress was 12 MPa before the earthquake, decreasing to 3-4 MPa after the earthquake.…”