Recovering Period of Postseismic Fluid Pressure in Fault Valve

The present study aims to reveal the recovering period of the postseismic fluid pressure in fault zone, offering an insight into earthquake recurrence. Numerical modeling is performed based on a 2D simple layered fault-valve model to simulate the fluid activities within the earthquake fault. In order to demonstrate the features of postseismic fluid pressure in natural state, the interference of tectonic movements is not considered. The recovering period of postseismic fluid pressure includes a sudden- changing period and a much longer fluctuating period. Modeling results show that fault permeability and porosity are sensitive parameters and reversely proportional to the recovering period of the fluid pressure in earthquake fault zone. When the permeability reduces from 10^-15 to 10^-18 m^2, the recovering period increases from 400 to 2 000 yrs, correspondently. The upper and lower fluid pressures are sepa- rated by the valve seal, causing their fluctuations in opposite tendencies.

Is clustered seismicity an indicator of regional stress?Insights from earthquake sequences in Yongning-Luguhu faulted basin,Southwest China

Using hypocenter relocation,moment tensor inversion,stress field inversion,and fault slip tendency analysis,this study systematically investigated three M5.5-5.8 earthquake sequences that occurred after 2000 in the Yongning-Luguhu faulted basin in the middle of the Lijiang-Xiaojinhe fault zone within the Sichuan-Yunnan block,Southwest China.Our results show that since the 2008 Wenchuan earthquake,the tectonic stress pattern in this area may have changed and that b-values estimated for the earthquake sequences show evidence of an increasing trend in stress in the study area.Seismicity in the small-scale faulted basin adjacent to the large-scale fault zone is a possible indicator of regional stress.We also note that the aftershocks of the M5.7 earthquake sequence in 2012 and the M5.5 earthquake sequence in 2022 show relatively clear fluid diffusion-triggering characteristics.Overpressure of deep fluids is still the main factor driving seismic activity in the region,and we propose that the background tectonic stresses have not yet reached critical levels.

Fluid-driven seismicity in relatively stable continental regions:Insights from the February 3^(rd),2020 M_(S)5.1 Qingbaijiang isolated earthquake

On February 3rd,2020,an isolated MS5.1 earthquake occurred in the northern section of the Longquanshan fault zone.This study aims at defining the geometry of seismogenic structures of this earthquake.In detail,centroid moment tensor inversion results show that the earthquake is characterized by a focal depth of 3.8 km with no corresponding surface faults.The strike/dip/rake angles for the two nodal planes are 205°/54°/96°and 15°/36°/82°,respectively.With the analyses of coseismic deformation of the surface obtained from InSAR measurements,together with the information of relocated hypocenters for a small number of aftershocks,it is concluded that a northwest-dipping nodal plane corresponds well to the source fault.The fault is suggested to have a length of about 2.8 km and a depth range of 2-5 km,and the centroid of the earthquake is located at 104.48°E and 30.71°N.Furthermore,multiple pieces of evidence indicate that this earthquake is partly driven by the overpressure effect associated with the adjacent natural gas packets,which is similar to several other moderate natural earthquakes in Sichuan Basin.