关键词: 景谷地震, 时移层析成像, 双差层析成像, P波速度变化

Abstract: Of methods for measuring temporal changes in seismic-wave speeds in the Earth,seismic tomography is among those that offer the highest spatial resolution. In order to obtain the high spatial resolution P-wave velocity changes in the hypocenter region of the 2014 Jinggu Ms6.6 earthquake. We use the seismic data in the hypocenter region of the Jinggu earthquake recorded by the Yunnan Digital Seismic Network from January 1, 2008 to December 31, 2017, and We first used the double-difference tomography method to invert the high-resolution three-dimensional P-wave velocity structure in the hypocenter region of the Jinggu earthquake by combining absolute and relative arrival time. The inversion results show that the aftershock sequence is distributed at the junction of the P-wave high-speed anomaly area and the low-speed anomaly area. The faults that intersect the Lancangjiang Fault is in the low-velocity anomaly zone, which may be related to the fluid in the faults. Then we used the time-lapse tomography method based on double-difference tomography to obtain the spatial and temporal distribution of P-wave velocity changes between different time periods. In addition, combining the results with the existing geological and geophysical researc, the characteristics and mechanism of P-wave velocity changes are explored, our results indicate that (1) The maximum decrease in P-wave velocity at the shallow depth near the epicenter of the main earthquake was 0.2%, which occurred two months after the main earthquake and was mainly affected by rock damage. (2) There is an area of P-wave velocity rise at the depth of 5km to 15km. It is speculated that this area is a brittle-ductile transition zone, and is not affected by the occurrence of the main shock. After the occurrence of Ms5.8 and Ms5.9 aftershocks on December 6, the distribution direction of aftershocks changed significantly, the depth of the source deepened, the brittle-ductile transition zone was affected by these two earthquakes so that the P wave velocity decreased to 3.8%. (3) About three years after the Jinggu earthquake, the P-wave velocity increase above the pre-earthquake level. The healing process in the hypocenter region may also include the stress accumulation process before the Ms5.9 earthquake in Mojiang, Yunnan on September 8, 2018.

Key words: Jinggu earthquake, Time-lapse seismic tomography, Double-difference seismic tomography, P-wave velocity changes