title: A Physics-Based Ground Motion Model for Induced Seismicity at Preston New Road Shale Gas Site, UK
Creators: name: Suroyo, Pungky
Publisher: name: University of Liverpool Repository
Year: 2024

description: Improving earthquake hazard assessment will enable more accurate risk management and mitigation strategies for technologies that lead to induced seismicity. However, the premise used in hazard assessment for regional tectonic earthquakes has the potential to be different from that for induced earthquake applications. A key question is, therefore, to understand the differences between induced and natural earthquakes, alongside factors influencing their resulting ground motions. This dissertation focuses on the study of seismic source, path, and site effects to develop a new Ground Motion Model (GMM) for induced seismicity. The objective is to improve our understanding regarding the applicability of existing Ground Motion Prediction Equations (GMPEs) and provide a local-specific GMPE for induced seismicity at the Preston New Road (PNR)-shale gas site. This is achieved through quantification of (i) seismic attenuation models and (ii) site-specific damping, and utilizing these models to (iii) simulate ground motions and develop local-specific GMPEs.

In the first study, the attenuation quality factor (Q) was estimated using the spectral analysis of induced and natural earthquake recordings. I investigate different attenuation behaviour between induced and regional earthquakes. Besides spectral analysis, a complementary technique, based on coda envelope decay, was used to support the conclusions. The results show that the local Q (obtained from the induced seismic sequences attributed to shallower layers in the crust), leads to rapid near-field amplitude decay, with significantly more substantial attenuation than observed for regional events. In addition to the path-attenuation model, through spectral analysis, a model of site-specific high-frequency diminution or kappa (κ) was determined.

The second part of the dissertation demonstrates the development of a physically-based GMM for induced seismicity. Both attenuation and diminution parameters obtained in the previous study were utilised as prior information to simulate ground motions at the PNR site along with other parameters such as earthquake stress drop, duration, and geometrical spreading. Calibration techniques using Area Metric (AM) were performed to produce the best combination of simulation-parameter models as an input to generate ground motions. Residual and covariance analyses were conducted to ensure the calibrated models generate a small bias between simulated and observed ground motions. The proposed combination of simulation-parameter models is then used to simulate synthetic ground motion data. We then combine the synthetic and observed ground motion data to produce a hybrid GMPE using a mixed-effects regression. I then evaluate the prediction accuracy by comparing the area metric misfit between the predicted and observed values using various GMPEs. 

In the final part of this thesis, I focus on high-frequency diminution (κ). This parameter is known to impact the ground motion from small earthquakes more substantially than those from large earthquakes. A relatively new method and not yet widely used, namely the spectral decay of ambient noise was evaluated to estimate the site-specific high-frequency attenuation parameters (κ0-noise). Estimates of κ0-noise are then compared to results from earthquake recordings (κ0-earthquakes). Challenges and limitations of this method were discussed along with a proposed approach for determining κ0- noise. This approach was then tested using noise recordings recorded at several stations in Switzerland and compared to existing measures.