Preliminary Results of In‐situ Stress Measurements along the Longmenshan Fault Zone after the Wenchuan M_s 8.0 Earthquake

Abstract

: Four months after the Wenchuan Ms 8 earthquake in western Sichuan, China, in situ stress measurements were carried out along the Longmenshan fault zone with the purpose of obtaining stress parameters for earthquake hazard assessment. In‐situ stresses were measured in three new boreholes by using overcoring with the piezomagnetic stress gauges for shallow depths and hydraulic fracturing for lower depths. The maximum horizontal stress in shallow depths (∼20 m) is about 4.3 MPa, oriented N19°E, in the epicenter area at Yingxiu Town, about 9.7 MPa, oriented N51°W, at Baoxing County in the southwestern Longmenshan range, and about 2.6 MPa, oriented N39°E, near Kangding in the southernmost zone of the Longmenshan range. Hydraulic fracturing at borehole depths from 100 to 400 m shows a tendency towards increasing stress with depth. A comparison with the results measured before the Wenchuan earthquake along the Longmenshan zone and in the Tibetan Plateau demonstrates that the stress level remains relatively high in the southwestern segment of the Longmenshan range, and is still moderate in the epicenter zone. These results provide a key appraisal for future assessment of earthquake hazards of the Longmenshan fault zone and the aftershock occurrences of the Wenchuan earthquake.

How Did the 2013 Lushan Earthquake (Ms = 7.0) Trigger its Aftershocks? Insights from Static Coulomb Stress Change Calculations

“…org/), strain rates computed from GPS observation (ZHU and SHI 2011), and in situ borehole stress measurements in which the stress regime is S Hmax [ S Hmin [ S v with the maximum horizontal compressive stress of 9.8 MPa oriented N51°W around the Lushan epicenter (WU et al 2009), will help us to ascertain the regional stresses in the DCFS computation. Moreover, WU et al (2009) presented that the stress level around the southwestern segment of the Longmen Shan fault was observed to be relatively high after the 2008 Wenchuan earthquake. Hence, one can see that the regional stress around the hypocenter of the Lushan earthquake is relatively complex.…”

Characteristics and implications of the stress state in the Longmen Shan fault zone, eastern margin of the Tibetan Plateau

“…1) that trend 40°N-50°E, with a total length of 500 km and width of 25-40 km. This zone contains the Maoxian-Wenchuan, Tectonophysics 656 (2015) 1-19 Pingwu-Qingchuan, Yingxiu-Beichuan, and Anxian-Guanxian faults (Xu et al, 2008;Dirks et al, 1994;Wu et al, 2009). The Longmen Shan fault zone has experienced the most devastating earthquake of the century, the 2008 M s 8.0 Wenchuan earthquake, which collapsed buildings and killed thousands in major cities in the western Sichuan Basin in China (Parsons et al, 2008).…”

Stress Build‐up in the Shallow Crust Before the Lushan Earthquake Based on the in Situ Stress Measurements

“…(14) is rewritten as follows: Fig. 3 Dependence of differential stress on effective mean stress at six locations where deep stress measurements have been performed (according to Townend & Zoback, 2000) The ratio of the maximum and minimum principal stresses is commonly employed in regional stability research in China (Wu et al, 2010). By comparing the principal stress ratio-limited by measured stresses-with the Byerlee frictional range, it can be determined whether the stress state can cause a crustal rupture.…”