Microseismicity Moment Tensor Estimation Using Surface and Downhole Geophone Arrays at Utah FORGE
Description:
Microseismicity associated with the 2022 spring stimulation at Utah FORGE exhibits magnitudes from -2 to 0. The concurrent passive seismic monitoring system was consisted of a dozen of downhole geophones along two wells and a ~200-geophone surface array. Geophones emplaced downhole within granite were < 1 km from the stimulation locations and the recorded seismicity waveforms have high signal-to-noise ratio (SNR). On the other hand, the surface array was generally ~2.5 km away deployed on the sediment layer, which causes high attenuation of signals and only events close to M0 are recorded with reasonable SNR. Despite the limitation, the surface array has strength of azimuthal coverage that is crucial for moment tensor solution. Therefore, in this study, we leverage complementary information from both geophone arrays based on their P polarities and amplitudes.
Beginning with the set of ~M0 events, for the surface array, we perform beamforming and a noise-suppression filter to align and enhance the incoming P energy, which outperforms linear stacking methods. Meanwhile, for the downhole array, we employ an SNR detection and visual inspection to identify the first arrivals. The resultant moment tensors reveal strike-slip mechanisms with fault strikes consistent with the known geologic formation. Next, we aim to retrieve the moment tensor for smaller events (< M0) that exhibit high similarity with the ~M0 events. To achieve this, we apply cluster analysis and waveform correlation. For the highly similar event (correlation coefficient larger than 0.9), we refine the SNR detection picks using correlation lag time for downhole data and we adapt the first arrival information from the corresponding surface data. We will further discuss the sensitivity from the aspects of first-arrival detection, moment-tensor inversion, and the applicability of the similarity-based method within this specific geothermal setting.
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: Sin-Mei
Student Presenter: No
Invited Presentation:
Authors
Sin-Mei Wu Presenting Author Corresponding Author a06859a35@gmail.com Lawrence Berkeley National Laboratory |
Nori Nakata nnakata@lbl.gov Lawrence Berkeley National Laboratory |
|
|
|
|
|
|
|
Microseismicity Moment Tensor Estimation Using Surface and Downhole Geophone Arrays at Utah FORGE
Session
Seismic Monitoring, Modelling and Management Needed for Geothermal Energy and Geologic Carbon Storage