In:
Frontiers in Earth Science, Frontiers Media SA, Vol. 10 ( 2023-1-19)
Abstract:
Current extensive seismicity in southern Sichuan Basin is ascribed to the reactivation of pre-existing faults, as a result of prolonged fluid injection for salt mining and shale gas development, respectively. However, the structural framework of the region remains poorly understood. Here, we apply V p /V s consistency-constrained double-difference seismic tomography to high quality phase data from 36,314 earthquakes jointly recorded by our local array and a regional seismic network to determine high-resolution velocity models. Earthquake relocations reveal shallow hypocenters for the M s & gt;5.0 earthquakes and two distinct seismogenic zones corresponding to the salt mine and shale gas regions, with most induced seismic events forming widespread lineaments some of which extend to the basement and are remarkably similar to the fault and fracture trends interpreted on reflection seismic and outcrops, respectively. Our 3-D crustal velocity analyses show that seismicity beneath the Changing salt mining area is associated with a combination of relatively low V p /V s (1.6–1.74) and high V p /V s (1.75–1.86) expressions, while most of small earthquakes within the Xingwen shale gas block are associated with relatively high V p /V s values (1.77–1.87), indicating the earthquakes in these two areas are caused by unique inducing mechanisms. The two moderately strong 2018 Xingwen M s 5.7 and 2019 Gongxian M s 5.3 earthquakes in the Xingwen shale gas block are located around low V p /V s . zones, suggesting they could be structurally controlled. In comparison, the 2019 Changning M s 6.0 earthquake in the Changning salt mining area is associated with high V p /V s . expression, suggesting its occurrence is related to fluid injections. In addition, top of the crystalline early Neoproterozoic (pre-Sinian) Sichuan basement is characterized by the 6.5 km/s V p contour, which is new for earthquake tomographic studies in the region. Combined with outcrop analysis, we are able to construct a structural framework for induced seismicity in southern Sichuan basin, which unravels the structural architecture of induced seismicity.
Type of Medium:
Online Resource
ISSN:
2296-6463
DOI:
10.3389/feart.2022.1082122
DOI:
10.3389/feart.2022.1082122.s001
Language:
Unknown
Publisher:
Frontiers Media SA
Publication Date:
2023
detail.hit.zdb_id:
2741235-0
Permalink
