The Interplay Between Fluid Injection, Aseismic Slip and Induced Microearthquakes Unveiled by Seismic Wave Analysis

Session: Mechanisms of Induced Seismicity: Pressure Diffusion, Elastic Stressing and Aseismic Slip
Type: Oral
Date: 4/29/2020
Time: 08:30 AM
Room: 215 + 220
Description: 

It is well known that fluid injection can induce earthquakes, but how fluid induces earthquakes initially and then contributes to the sequences of earthquakes following afterwards are still puzzling. Using the spectral ratio method based on empirical Green’s functions, we analyze source parameters of Mw −3.9 to −3.1 induced earthquakes during an in-situ fluid injection experiment in France. The induced microearthquakes were preceded by considerable aseismic deformation that accounted for 99.9% of the energy budget. Our analysis has revealed unprecedent details of the interplay of fluid injection and seismicity migration. We show that the microearthquakes ruptured meter-scale source patches with <1‐μm slip in a preexisting fracture network oriented differently from the injected plane. Five out of eight master events occurred at the peak of injection pressure, indicating the meter-scale faults ruptured at a critical pressure level. Focal mechanism analysis has unveiled two primary sets of fracture planes that host earthquakes alternatively, as if rupture on one fracture might unlock the aseismic motion and increase stress on the remaining ones. The relative stress drops of microearthquakes in the experiment fall in the low end of those of central U.S. induced earthquakes, suggesting the aseismic deformation may have released a considerable amount of stress before seismicity was induced.

Presenting Author: Yihe Huang

Authors