About

Dr. Xiaowei Chen is an Associate Professor in the Department of Geology and Geophysics at Texas A&M University. He holds the Robert Berg Professorship in Geology and Geophysics and is known for his research in geophysics and geology. His work focuses on the study of the Earth's interior, including seismic imaging and the dynamics of the mantle and crust.

Research topics

• Physics
• Atomic physics
• Crystallography
• Computer science
• Environmental health

Selected publications

• Comparison of EGF Methods for Ridgecrest Sequence: Can EGFs Help Resolve Ambiguity in Isolating Source Spectra?

  Bulletin of the Seismological Society of America · 2025-03-04 · 6 citations

  article

  ABSTRACT The spectral stress drop is a popular parameter for the simple quantification and characterization of an earthquake source and its expected seismic radiation, enabling investigation of earthquake spatial and temporal variability for larger numbers of events. In addition, spectral measurements are one of the few possible for earthquake characterization and hazard prediction in regions of low seismicity. However, spectral stress-drop estimates are uncertain, especially as recorded earthquakes may be too complex to characterize ideally with a single parameter. Empirical Green’s function (EGF) approaches to isolate the earthquake source are widely regarded as one of the best for individual analysis of well-recorded earthquakes. However, analysis decisions related to the selection of stations, EGFs, time windows, frequency bandwidth, and source models can cause discrepancies in resulting estimates of the source spectrum, source time function, and source parameters. We present results following one well-developed EGF approach, and compare it with those from three other independent methods applied to earthquakes in the 2019 Ridgecrest, California, earthquake, sequence selected for the Southern California Earthquake Center /U.S. Geological Survey Community Stress Drop Validation Study. The common data set consists of two weeks of earthquakes from the 2019 Ridgecrest earthquake sequence, including nearly 13,000 events of M 1 and greater, recorded on stations within 100 km. We obtain estimates of corner frequency and spectral stress drop for 75 earthquakes (M 2.2–4.6) and find varying degrees of similarity among studies. We investigate four events in detail (M 2.7–4.1) and find that we obtain consistent results when the sources are relatively simple. Multiple EGFs produce good ratios and source time functions at stations with good azimuthal distribution. This suggests that there is a role for such approaches to resolve the inherent ambiguity in larger scale inversions between source scaling and attenuation and site effects.

  PublisherDOI

• Factors That Influence Variability in Stress-Drop Measurements Using Spectral Decomposition and Spectral-Ratio Methods for the 2019 Ridgecrest Earthquake Sequence

  Bulletin of the Seismological Society of America · 2025-04-21 · 6 citations

  article1st authorCorresponding

  ABSTRACT Stress drop is a fundamental parameter related to earthquake source physics, but is hard to measure accurately. To better understand how different factors influence stress-drop measurements, we compare two different methods using the Ridgecrest stress-drop validation data set: spectral decomposition (SD) and spectral ratio (SR), each with different processing options. We also examine the influence of spectral complexity on source parameter measurement. Applying the SD method, we find that frequency bandwidth and time-window length could influence spectral magnitude calibration, while depth-dependent attenuation is important to correctly map stress-drop variations. For the SR method, we find that the selected source model has limited influence on the measurements; however, the Boatwright model tends to produce smaller standard deviation and larger magnitude dependence than the Brune model. Variance reduction threshold, frequency bandwidth, and time-window length, if chosen within an appropriate parameter range, have limited influence on source parameter measurement. For both methods, wave type, attenuation correction, and spectral complexity strongly influence the result. The scale factor that quantifies the magnitude dependence of stress drop show large variations with different processing options, and earthquakes with complex source spectra deviating from the Brune-type source models tend to have larger scale factor than earthquakes without complexity. Based on these detailed comparisons, we make a few specific suggestions for data processing workflows that could help future studies of source parameters and interpretations.

  PublisherDOI

• Focal Mechanism and Stress Analysis of the CAPE Site, Utah

  2025-10-15 · 1 citations

  preprintOpen access

  Microseismic monitoring plays a pivotal role in characterizing subsurface dynamics and assessing induced seismicity risks in Enhanced Geothermal Systems (EGS). This study presents a comprehensive analysis of microseismic data from the Cape Modern EGS field in Southwest Utah, where three horizontal wells underwent plug-and-perf hydraulic stimulation. The monitoring infrastructure comprised an integrated network of shallow borehole sensors, surface nodal arrays, deep borehole fiber optic sensors, and three-component passive sensors, capturing over 7,000 events during the February-March 2024 stimulation period. We implemented a multi-faceted analytical approach, beginning with phase arrival prediction and first motion polarity determination utilized deep learning techniques, while focal mechanism estimation employed the SKHASH method, incorporating P-wave polarity and S/P amplitude ratios. This methodology yielded 2,091 focal mechanism solutions, with 1,564 achieving high-quality (A and B) classifications. Subsequent clustering analysis using UMAP-HDBSCAN revealed four distinct structural features, with Structure D exhibiting complex spatial patterns and multiple subclusters. Stress field analysis using MSATSI demonstrated significant spatial heterogeneity, transitioning from strike-slip dominated regimes in the western section (SHmax 15-30° from North) to reverse faulting patterns in the eastern section (SHmax 0-15° from North). The stress ratio variations indicate complex mechanical interactions between stimulation operations and local geological structures. These findings provide crucial insights for optimizing EGS operations while highlighting the effectiveness of integrating machine learning techniques with traditional geophysical methodologies for enhanced reservoir characterization.

  PublisherOA PDFDOI

• Overview of the SCEC/USGS Community Stress Drop Validation Study Using the 2019 Ridgecrest Earthquake Sequence

  Bulletin of the Seismological Society of America · 2025-05-02 · 20 citations

  article

  ABSTRACT We present initial findings from the ongoing Community Stress Drop Validation Study to compare spectral stress-drop estimates for earthquakes in the 2019 Ridgecrest, California, sequence. This study uses a unified dataset to independently estimate earthquake source parameters through various methods. Stress drop, which denotes the change in average shear stress along a fault during earthquake rupture, is a critical parameter in earthquake science, impacting ground motion, rupture simulation, and source physics. Spectral stress drop is commonly derived by fitting the amplitude-spectrum shape, but estimates can vary substantially across studies for individual earthquakes. Sponsored jointly by the U.S. Geological Survey and the Statewide (previously, Southern) California Earthquake Center our community study aims to elucidate sources of variability and uncertainty in earthquake spectral stress-drop estimates through quantitative comparison of submitted results from independent analyses. The dataset includes nearly 13,000 earthquakes ranging from M 1 to 7 during a two-week period of the 2019 Ridgecrest sequence, recorded within a 1° radius. In this article, we report on 56 unique submissions received from 20 different groups, detailing spectral corner frequencies (or source durations), moment magnitudes, and estimated spectral stress drops. Methods employed encompass spectral ratio analysis, spectral decomposition and inversion, finite-fault modeling, ground-motion-based approaches, and combined methods. Initial analysis reveals significant scatter across submitted spectral stress drops spanning over six orders of magnitude. However, we can identify between-method trends and offsets within the data to mitigate this variability. Averaging submissions for a prioritized subset of 56 events shows reduced variability of spectral stress drop, indicating overall consistency in recovered spectral stress-drop values.

  PublisherDOI

• Detection of Overpressured and Hydrocarbon-Bearing Zones Using the Normalized Second Harmonic Peak Index (NSHPI): Case Studies from the Illinois Basin and Offshore Nova Scotia.

  Abstracts with programs - Geological Society of America · 2025-01-01

  articleSenior author
  PublisherDOI

• Effect of Time Window and Spectral Measurement Options on Empirical Green’s Function Analysis Using DAS Array and Seismic Stations

  Bulletin of the Seismological Society of America · 2025-03-04 · 6 citations

  article1st authorCorresponding

  ABSTRACT The recorded seismic waveform is a convolution of event source term, path term, and station term. Removing high-frequency attenuation due to path effect is a challenging problem. Empirical Green’s function (EGF) method uses nearly collocated small earthquakes to correct the path and station terms for larger events recorded at the same station. However, this method is subject to variability due to many factors. We focus on three events that were well recorded by the seismic network and a rapid response distributed acoustic sensing (DAS) array. Using a suite of high-quality EGF events, we assess the influence of time window, spectral measurement options, and types of data on the spectral ratio and relative source time function (RSTF) results. Increased number of tapers (from 2 to 16) tends to increase the measured corner frequency and reduce the source complexity. Extended long time window (e.g., 30 s) tends to produce larger variability of corner frequency. The multitaper algorithm that simultaneously optimizes both target and EGF spectra produces the most stable corner-frequency measurements. The stacked spectral ratio and RSTF from the DAS array are more stable than two nearby seismic stations, and are comparable to stacked results from the seismic network, suggesting that DAS array has strong potential in source characterization.

  PublisherDOI

• Sequential Fracture Activation and Stress Evolution During EGS Stimulation at Utah FORGE Revealed by Waveform Cross-Correlation

  2025-10-12

  preprintOpen access

  Mapping fracture networks in Enhanced Geothermal Systems (EGS) is essential for optimizing reservoir performance, yet their complex evolution during stimulation remains difficult to resolve. This study examines the evolution of microseismicity and fracture networks during stage 3 of the 2022 EGS stimulation at the Utah FORGE site. We map the fracture network represented by 20 clusters of seismic events identified by waveform similarities with cross-correlation. We characterize their geometric properties, such as strike, dip, length, and width, and analyze the time evolution of activated fractures. The results reveal a systematic fracture evolution: early activation of pre-existing natural fractures, complex network development during peak injection, and continued activation of less favorably oriented fractures post-injection. Magnitude calibration using the Principal Component Analysis (PCA) of cross-correlated waveforms improves relative amplitude measurements, refining estimations of the Gutenberg-Richter b-values with spatial variations in b-values suggesting stress redistribution across the stimulated area. Analysis of the stress state of selected fractures further shows that fractures requiring higher excess pore pressure primarily activate at the end of injection and post-injection, highlighting stress transfer due to pore pressure as a dominant triggering mechanism. These findings provide insights into fracture propagation, stress evolution, and seismic hazard assessment in EGS reservoirs.

  PublisherOA PDFDOI

• Earthquake Source Spectra Estimates Vary Widely for Two Ridgecrest Aftershocks Because of Differences in Attenuation Corrections

  Bulletin of the Seismological Society of America · 2024-12-06 · 22 citations

  article

  ABSTRACT Differences in stress-drop estimates among groups of scientists for the same earthquakes suggest disagreement in the shape of the source spectra that are used to measure corner frequency. A critical step in characterizing source spectra involves applying empirical corrections for site effects and the loss of high-frequency energy that occurs along the source–receiver path. As part of the Ridgecrest stress-drop validation study, we compare path-corrected source spectra among different methods for two nearly collocated M 3 earthquakes and investigate whether systematic differences in the applied path corrections are affecting corner-frequency estimates. We find substantial disagreements in the path corrections, which are well approximated with a simple exponential function related to the strong ground motion parameter κ. These κ differences are strongly correlated with corner-frequency estimates for path-corrected spectra, suggesting they are a large source of systematic differences in corner frequency (and inferred stress drop) among the methods, reflecting varying trade-offs between the source and path contributions to observed spectra. Because each method presumably fits the data it uses sufficiently well, these results indicate the limitations of existing purely empirical techniques to estimating path corrections and the need for new approaches.

  PublisherDOI

• Precise relative magnitude measurement improves fracture characterization during hydraulic fracturing

  Geophysical Journal International · 2024-06-07 · 4 citations

  articleOpen access

  SUMMARY Microseismic monitoring is an important technique to obtain detailed knowledge of in-situ fracture size and orientation during stimulation to maximize fluid flow throughout the rock volume and optimize production. Furthermore, considering that the frequency of earthquake magnitudes empirically follows a power law (i.e. Gutenberg–Richter), the accuracy of microseismic event magnitude distributions is potentially crucial for seismic risk management. In this study, we analyse microseismicity observed during four hydraulic fracture treatments of the legacy Cotton Valley experiment in 1997 at the Carthage gas field of East Texas, where fractures were activated at the base of the sand-shale Upper Cotton Valley formation. We perform waveform cross-correlation to detect similar event clusters, measure relative amplitude from aligned waveform pairs with a principal component analysis, then measure precise relative magnitudes. The new magnitudes significantly reduce the deviations between magnitude differences and relative amplitudes of event pairs. This subsequently reduces the magnitude differences between clusters located at different depths. Reduction in magnitude differences between clusters suggests that some attenuation-related biases could be effectively mitigated with relative magnitude measurements. The maximum likelihood method is applied to understand the magnitude frequency distributions and quantify the seismogenic index of the clusters. Statistical analyses with new magnitudes suggest that fractures that are more favourably oriented for shear failure have lower b-value and higher seismogenic index, suggesting higher potential for relatively larger earthquakes, rather than fractures subparallel to maximum horizontal principal stress orientation.

  PublisherOA PDFDOI

• An improved estimation of stress drop and its application on induced earthquakes in the Weiyuan Shale Gas Field in China

  Geophysical Journal International · 2024-01-03 · 12 citations

  articleOpen accessSenior author

  SUMMARY Stress drop is a proxy of understanding earthquake source process, and it is controversial whether the stress drops of induced earthquakes associated with hydraulic fracturing and injection activities are similar to those of tectonic earthquakes. The measurement of stress drops is usually biased due to the limitations of observation means, or hidden issues in the estimation approaches. Utilizing a local short-period seismic network, we investigate the stress drops of induced earthquakes in Weiyuan Shale Gas Field in Sichuan Province, China from 2019 to 2020. Totally 11 844 earthquakes are involved in the analysis, and their stress drops are obtained using an improved approach on the basis of the traditional spectral decomposition method combined with a global optimization algorithm to avoid stacking of spectra that is found leading to source parameter underestimation. We divide the studied area into three subareas, and the results show strong stress drop heterogeneity across the entire region. We obtain an average stress drop of 2.29 MPa, piecewise stress drop dependence to earthquake magnitude, and complex depth dependence pattern. Our results indicate that stress drops of induced earthquakes are overall consistent with the induced earthquakes in other areas as well as tectonic earthquakes in different environments. Meanwhile, the complexity in the stress drop dependence to depth possibly reflects the variability of stress drops for different earthquake triggering mechanisms.

  PublisherOA PDFDOI

Frequent coauthors

• Y.-W. Lui

  Texas A&M University

  11 shared

• Y. Tokimoto

  Texas A&M University

  10 shared

• D. H. Youngblood

  Texas A&M University

  9 shared

• H. L. Clark

  8 shared

• B. V. John

  5 shared

• T. Al-Abdullah

  King Fahd University of Petroleum and Minerals

  4 shared

• J. Button

  National Center for Environmental Health

  3 shared

• Krishichayan

  3 shared

Labs

• Xiaowei ChenPI

Awards & honors

• Stubbeman-Drace Presidential Professor, University of Oklaho…
• Editor's citation for excellence in refereeing for JGR-Solid…