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Application of Static Stress Drops and Similarity of Seismic Events Induced by Underground Fluid Injection in Characterization of Seismogenic Zones on the Example of The Geysers Geothermal Field

Description: 

Characterization of seismogenic zones in the areas of underground fluid injection is an important issue for seismic hazard assessment in such destinations. It is well known that subsurface discontinuities can be successfully imaged using multiplets, i.e. seismic events with very similar waveforms. On the other hand, recently static stress drop of earthquakes has been suspected to reflect the strength of rocks. In this study we propose to utilize combined information from spatiotemporal multiplet analysis and statistical assessment of static stress drop variability to characterize the origin zones of injection induced seismicity. As an example, we present results obtained using dataset from Prati-9 and Prati-29 injection wells at The Geysers geothermal field. With the use of multiplet analysis followed by double-difference relocation we imaged three fractures and one fault within the reservoir and described their different seismic response to injection. Moreover, we statistically proved the occurrence of independent spatial and temporal variations of static stress drop of events and interpreted them as an image of differences in strength of discontinuities. Obtained results prove the fact that the information obtained from multiplet and stress drop analyses is complementary and can be interpreted together. In order to check the utility of proposed method for the purposes of hazard assessment, we related the locations of the strongest events in the cluster to identified discontinuities. Moreover, we assessed the maximum expected magnitude basing on the dimensions of identified fault. Finally, we calculated the effect of analyzed events on the surface (PGV, PHV, PVV) and related obtained values to observed stress drop differences. This research was supported by research project no. 2022/45/N/ST10/02172, funded by the National Science Centre, Poland, under agreement no. UMO-2022/45/N/ST10/02172. This work was also partially supported by a subsidy from the Polish Ministry of Education and Science for the Institute of Geophysics, Polish Academy of Sciences. This research was supported in part by PLGrid Infrastructure.

Session: Seismic Monitoring, Modelling and Management Needed for Geothermal Energy and Geologic Carbon Storage [Poster Session]

Type: Poster

Date: 5/2/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Monika

Student Presenter: No

Invited Presentation: 

Authors