Models Of Crustal Deformation Research Articles

Real-time modeling of transient crustal deformation through the quantification of uncertainty deduced from GNSS data

We propose a new method for real-time uncertainty monitoring of earthquake and volcano source models using data from the global navigation satellite system (GNSS) and explore its application concerning observation station placement. The Geospatial Information Authority of Japan operates two main types of GNSS earth observation network system (GEONET) coordinates for crustal deformation monitoring on different time scales: post-processing analysis values and real-time GEONET analysis system for rapid deformation monitoring (REGARD). REGARD uses the Markov Chain Monte Carlo (MCMC) method termed real-time automatic uncertainty estimation of a coseismic single rectangular model using GNSS data (RUNE) for single rectangular fault model estimation to handle uncertainty. Thus far, no GNSS monitoring system can automatically detect transient crustal deformation events, such as volcanic activity and earthquake swarms, on timescales of a day or less. We extended RUNE and developed a core program for a new monitoring system for earthquake and volcanic source models and their uncertainties. Our program achieved automatic and stable MCMC utilization for rectangular fault, dike, Mogi, and spheroid models by increasing the computational speed, improving search efficiency, and adjusting hyperparameters. The program automatically determines the standard deviation of the likelihood function assuming a normal distribution with weights for each observation station. The calculation time was within 15 s for 1 × 106 samples on a standard 1U server. We assessed the reliability of the developed method using synthetic and observed GNSS data from the 2015 Sakurajima volcanic event. The results were consistent with the assumed model and previous studies and indicated an advantage in automatically quantifying uncertainty in a short computation time. Based on MCMC samples, we developed a new visualization algorithm to indicate areas on a map in which the number of observation stations should be expanded. We assessed the reliability using data from the 2023 Noto Peninsula earthquake [Mj 6.5]. The results indicate that the algorithm is helpful in studying the placement of stations. The above model extensions and their application are essential to achieve a rapid quantitative understanding of disaster events near urban areas and for utilizing this information in emergency response activities.Graphical

The Impact of the Three-Dimensional Structure of a Subduction Zone on Time-dependent Crustal Deformation Measured by HR-GNSS

Accurately modeling time-dependent coseismic crustal deformation as observed on high-rate Global Navigation Satellite System (HR-GNSS) lends insight into earthquake source processes and improves local earthquake and tsunami early warning algorithms. Currently, time-dependent crustal deformation modeling relies most frequently on simplified 1D radially symmetric Earth models. However, for shallow subduction zone earthquakes, even low-frequency shaking is likely affected by the many strongly heterogeneous structures such as the subducting slab, mantle wedge, and the overlying crustal structure. We demonstrate that including 3D structure improves the estimation of key features of coseismic HR-GNSS time series, such as the peak ground displacement (PGD), the time to PGD (tPGD), static displacements (SD), and waveform cross-correlation values. We computed synthetic 1D and 3D, 0.25 Hz and 0.5 Hz waveforms at HR-GNSS stations for four M7.3+ earthquakes in Japan using MudPy and SW4, respectively. From these synthetics, we computed intensity-measure residuals between the synthetic and observed GNSS waveforms. Comparing 1D and 3D residuals, we observed that the 3D simulations show better fits to the PGD and SD in the observed waveforms than the 1D simulations for both 0.25 Hz and 0.5 Hz simulations. We find that the reduction in PGD residuals in the 3D simulations is a combined effect of both shallow and deep 3D structures; hence incorporating only the upper 30 km of 3D structure will still improve the fit to the observed PGD values. Our results demonstrate that 3D simulations significantly improve models of GNSS waveform characteristics and will not only help understand the underlying processes, but also improve local tsunami warning.

Seismotectonics of the San Andreas Fault System in the San Gorgonio Pass region: A synthesis

In the San Gorgonio Pass region of Southern California, USA, the San Andreas fault exhibits greater geometric complexity than anywhere else along its length, with multiple nonparallel fault strands that branch and join both laterally and at depth (Fig. 1). These structures are associated with regional contraction within the San Gorgonio Pass region due to the nearby Big Bend of the San Andreas fault. The complexity of past and present faulting in this region has led Jon Matti, Doug Yule, and others to call this the “San Gorgonio knot.” Due to its complexity, this part of the San Andreas fault system may serve as both a barrier and an initiation point for devastating earthquakes. Research to understand and unravel the San Gorgonio knot has important implications for seismic hazard in southern California. The first author of this manuscript, Doug Yule, investigated slip rates and earthquake records in this enigmatic region from the mid-1990s until his death in 2022 (Fig. 2). During the 2010s, many researchers, including co-authors Cooke and Oglesby, were inspired by Doug Yule’s work in this area. Together, the three authors coordinated a five-year research effort to investigate active faulting within the San Gorgonio Pass, involving many researchers in the Southern California Earthquake Center (SCEC) community with support from SCEC, their various organizations, and institutions. Many of the results of this effort are compiled in this Geosphere thematic issue, with 11 papers that span earthquake geology, geomorphology, geodesy, potential field geophysics, crustal deformation models, and dynamic rupture models. Here, we highlight findings from these studies and honor the role that Doug played in bringing together earthquake scientists from a variety of disciplines to better understand the rupture potential through the complex faults of the San Gorgonio Pass. Much of this science can be organized around a few key questions.

Modeling of Crustal Deformation Due To Sumatra Tectonic Earthquakes Based On GNSS Remote Sensing Data

Indonesia is at the confluence of three large plates, so it often experiences earthquakes. Therefore, earthquake disaster mitigation efforts must be increased. One of the efforts that can help the government prepare a disaster mitigation system for earthquakes and their associated disasters is research on fault deformation. This research utilizes continuous data from the Global Navigation Satellite System (GNSS), especially the Global Positioning System (GPS), which is processed into surface deformation. The crustal deformation was modeled based on the Okada formulation with estimated earthquake parameters and then verified with surface deformation to obtain optimal parameter values. Automation is carried out with a computerized system to speed up the estimation process, and more optimal results are obtained using the Hooke-Jeeves numerical method. We do modeling for tectonic earthquakes in Sumatra during 2005 and 2007 with magnitudes > 8 Mw. The modeling results were validated with seismic data and seismological theory of the seismic moment. The success of this modeling can be taken into consideration in earthquake prediction as part of an earthquake disaster mitigation system.

U-Pb ages of Gongga Shan granite, western Sichuan and its implication to the tectonic evolutions of eastern Tibet

The eastern margin of the Tibetan Plateau has given rise to much debate about mechanisms of plateau uplift and evolution and, in particular, the role of the lower crust in crustal thickening. Knowledge of the middle to lower crust conditions is critical for evaluating various models of crustal deformation, but data on crustal evolution through time are lacking. Here, we turn to the Gongga Shan granite, an intrusion along the Xianshuihe fault in easternmost Tibet that directly records local Cenozoic crustal conditions. We present 124 U-Pb samples from the Gongga Shan granite (GSG) that prove that the crust has been stepwise producing partial melt from 56 Ma to 4 Ma. According to the age distribution, the GSG can be separated into four major groups with ages of 4–10 Ma, 12–20 Ma, 25–40 Ma, and 43–56 Ma. Combining the timing information with geophysics and low-temperature thermochronology data, we suggest that events younger than 10 Ma may indicate the onset of recent crustal channel flow in the middle to lower crust. In contrast, the youngest 4 Ma ages indicate the ongoing partial melting of the middle crust. The 12–20 Ma events could be related to an earlier stage of crustal channel flow, consistent with the regional large-scale crustal channel flow in central Tibet.

Mechanical Analysis of Fault Slip Rate Sites within the San Gorgonio Pass Region, Southern California USA

Earthquake hazard assessments rely on observations from the field and geophysical data that provide fault slip rate estimates at specific sites and inform the geometry of active faults; however, uncertainty remains for both slip rate and geometry. Furthermore, incompatibilities between inferred fault geometry and geologic slip rates arise within crustal deformation models where model and geologic slip rates disagree. The impact of these incompatibilities may be local to sites or have wider effect on the fault system deformation. Here, we investigate the roles of structural position of sites and uncertainty of slip rates using three-dimensional mechanical models that simulate deformation across many earthquake cycles along southern San Andreas fault near the San Gorgonio Pass in California. Within the models, the impact of strike-slip rate sites on the fault system depends on their structural positions. Slip rates at sites along short and segmented faults has lesser impact on the slip along the fault system than either slip rates at sites along longer faults or at sites within fault branches. Consequently, inaccuracies in the slip rate estimates used for seismic hazard assessment may have differing impacts on the fault system depending on location and structural position of the slip rates. Fault branches along strike-slip faults warrant detailed investigation not only because these areas have high spatial variability of slip rate and accrue nearby off-fault deformation but also because changes in slip rates along branches has larger impact on deformation along fault system than other sites. Lack of data or large uncertainty in slip rate data from fault branches can affect our ability to accurately assess seismic hazard of the region.

Measurements of Rayleigh wave ellipticity anisotropy and implications for distinct crustal deformation styles across the SE Tibet margin

Plateau growth of southeastern Tibet is often understood by applying the end-member conceptual models, such as ductile material flow in the deep crust, and lateral extrusion of coherently deforming or rigid blocks. Though recent studies suggest the local crustal flow and movements of rigid blocks may be compatible in a way, ambiguities still persist in the formation of the gently sloping margin of southeastern Tibet and interactions between the plateau and the outer forelands. Here we present a 3D crustal deformation model in southeastern Tibet and adjacent regions, by summarizing different types of seismic anisotropy measurements including a newly obtained continuous map of uppermost crustal anisotropy, which are derived from observations of the directionally dependent teleseismic Rayleigh wave ellipticity. Layered deformation is observed within the crust beneath the southeastern Tibet Plateau, while the outer foreland shows an overall coherently deforming mode. The conspicuous change of the crustal deformation styles across the southeastern Tibet margin is against the idea that the low topographic gradients of the plateau margin were produced by leakage of ductile deep crust beneath the plateau. We argue that both the crustal flow beneath the plateau interior and lateral extrusion of the outer foreland accommodate the intracontinental convergence at southeastern Tibet.

A Fault-Based Crustal Deformation Model with Deep Driven Dislocation Sources for the 2023 Update to the U.S. National Seismic Hazard Model

Abstract A fault-based crustal deformation model with deep driven dislocation sources is applied to estimate long-term on-fault slip rates and off-fault moment rate distribution in the western United States (WUS) for the 2023 update to the National Seismic Hazard Model (NSHM). This model uses the method of Zeng and Shen (2017) to invert for slip rate and strain-rate parameters based on inputs from Global Positioning System (GPS) velocities and geologic slip-rate constraints. The model connects adjacent major fault segments in California and the Cascadia subduction zone to form blocks that extend to the boundaries of the study area. Faults within the blocks are obtained from the NSHM geologic fault section database. The model slip rates are determined using a least-squares inversion with a normalized chi-square of 6.6. I also apply a time-dependent correction called “ghost transient” effect to account for the viscoelastic responses from large historic earthquakes along the San Andreas fault and Cascadia subduction zone. Major discrepancies between model slip rates and geologic slip rates along the San Andreas fault, for example, from the Cholame to the Mojave and San Bernardino segments of the San Andreas, are well reduced after the ghost transient correction is applied to GPS velocities. The off-fault moment rate distribution is consistent with regional tectonics and seismicity patterns with a total rate of 1.6×1019 N·m/yr for the WUS.

The effects of pre-stress assumptions on dynamic rupture with complex fault geometry in the San Gorgonio Pass, California, region

Abstract We use three-dimensional (3-D) dynamic finite-element models to investigate potential rupture paths of earthquakes propagating along faults through the western San Gorgonio Pass, a structurally complex region along the San Andreas fault system in southern California (USA). We focus on the right-lateral San Bernardino strand of the San Andreas fault system, the oblique thrust–right-lateral San Gorgonio Pass fault zone, and a portion of the right-lateral Garnet Hill strand of the San Andreas fault system. We use the 3-D finite-element method to model rupture propagation along a fault geometry that reflects current understanding of the local geometrical complexity and is consistent with long-term loading and observed surface deformation. We test three different types of pre-stress assumptions: (1) constant tractions (assuming pure right-lateral strike-slip motion on the San Bernardino and Garnet Hill strands and oblique thrust–right-lateral strike-slip motion on the San Gorgonio Pass fault zone), (2) a uniform regional stress regime, and (3) long-term (evolved) stress from quasi-static crustal deformation modeling. Our results imply that under the more realistic regional stress and evolved stress assumptions, throughgoing rupture propagation from the southeast to northwest (i.e., from the Garnet Hill to the San Bernardino strand) may be more likely than throughgoing rupture in the reverse direction (from the San Bernardino to the Garnet Hill strand). The results may have implications for the earthquake potential in the region as well as for ground motion in the Los Angeles Basin. The results also emphasize how fault geometry and stress patterns combine to influence rupture propagation on complex fault systems.

Viscoelastic Fault-Based Model of Crustal Deformation for the 2023 Update to the U.S. National Seismic Hazard Model

Abstract The 2023 update to the National Seismic Hazard (NSHM) model is informed by several deformation models that furnish geodetically estimated fault slip rates. Here I describe a fault-based model that permits estimation of long-term slip rates on discrete faults and the distribution of off-fault moment release. It is based on quantification of the earthquake cycle on a viscoelastic model of the seismogenic upper crust and ductile lower crust and mantle. I apply it to a large dataset of horizontal and vertical Global Positioning System (GPS) interseismic velocities in the western United States, resulting in long-term slip rates on more than 1000 active faults defined for the NSHM. A reasonable fit to the GPS dataset is achieved with a set of slip rates designed to lie strictly within a priori geologic slip rate bounds. Time-dependent effects implemented via a “ghost transient” have a profound effect on slip rate estimation and tend to raise calculated slip rates along the northern and southern San Andreas fault by up to several mm/yr.

NeoKinema Deformation Model for the 2023 Update to the U.S. National Seismic Hazard Model

Abstract We develop a crustal deformation model of the western conterminous United States for the 2023 update of the National Seismic Hazard Model (NSHM). The kinematic finite-element code NeoKinema is used to describe crustal deformation, including long-term slip on faults and off-fault strains (both elastic and permanent). Three different data sets—Global Positioning System (GPS) velocities, geological fault offset rates, and crustal stress orientations—are used to constrain the model, and the plate tectonic rotation of Pacific relative to North America is also imposed on some boundaries. Compared to the last NSHM model update in 2014, the GPS and geological fault data are substantially updated, and new corrections are implemented in both the data and modeling approach, including the correction of the “ghost transient” effect due to postseismic deformation following large historic earthquakes, and correction for shallow creep on faults estimated from independent data. Based on these modeling results and a plate tectonic model of the Cascadia subduction zone, a long-term seismicity rate map is also computed for the western United States; this map is independent of the local seismic catalog and can, therefore, be tested retrospectively as well as prospectively. We find good success in most of the region, except in Cascadia, where the 45 yr instrumental seismicity record is much quieter than the forecast of our long-term model.

Holocene Slip Rate Along the Beng Co Fault and Dextral Strike‐Slip Extrusion of Central Eastern Tibet

AbstractThe dearth of quantitative studies of Holocene fault slip‐rates makes kinematic modeling of crustal deformation across SE Tibet debatable. The ∼230 km long, WNW‐striking, dextral Beng Co fault (BCF) is the most prominent strike‐slip fault of southern Tibet. Using new UAV topographic data and OSL/14C dating of geomorphic markers, we measure horizontal offsets and ages of fluvial terraces/fans and lacustrine shorelines at eight sites west and east of the Beng Lake pull‐apart. Along the eastern BCF's northern branch, our measurements at two different locations are consistent with offsets of ∼4.7 ± 1.1 and ∼8.7 ± 0.7 m during the past ∼3.1–3.6 and 3.6–5.2 ka, respectively. Along the southern branch, ∼25 ± 5 m of slip have accrued since ∼9 ka. The total Holocene slip‐rate across both faults (4.2–5.4 or 4.8 ± 0.5 mm/yr), consistent with GPS/InSAR values, implies that the BCF contributes significantly to the eastward extrusion of eastern‐central Tibet. This rate is slightly larger than the lower bound of the extension rate (∼6 ± 1.8 mm/yr) recently determined across the middle Gulu rift normal fault, which splays off southwards from the southeastern tip of the BCF's southern branch. Empirical relationships suggest that the reported ∼90 km length of theMw7.7, 1951 Beng Co earthquake surface rupture is too short, which implies that the eastern BCF is immature, or requires additional, partly deep slip, along other branches of the eastern BCF. That there is no field evidence of rupturing along the western BCF in the last ∼1,000 yr indicates that the Bange County area, west of Beng Co, may be at risk of anMw ≈ 7.4? event.

Active crustal deformation model of the Fen–Wei rift zone, North China: Integration of geologic, geodetic, and stress direction datasets

The Fen–Wei rift zone (FWRZ) of North China is an important zone of active crustal deformation representing a transition from extrusion tectonics related to the Tibetan Plateau to subduction tectonics related to the potential far-field influence of the west Pacific plate. In this study, we determined the kinematic constraints of active crustal deformation in the FWRZ, which are fundamental for forecasting seismicity. NeoKinema, a kinematic finite-element model, was employed to estimate the long-term fault slip rates, distributed crustal deformation field, and on- and off-fault strain-rate fields in the FWRZ by fitting updated geological fault slip rate, geodetic GPS velocity, and principal compressive stress direction datasets. Our results show that the FWRZ is a characteristic low-strain kinematic setting, with most active faults exhibiting slip rates of less than 1 mm/a. The total sinistral shear rate from the southern Ordos block to the Qinling Mountains is approximately 1 mm/a, indicating limited tectonic extrusion along the EW-trending Qinling Mountains. Additionally, the central Shanxi rift exhibits prominent dextral shear of ∼0.5 mm/a that decreases toward its north and south ends, corresponding to crustal extension of 1.1–1.2 mm/a in the Datong and Yuncheng basins, respectively. However, this significant crustal extension cannot be solely attributed to terminal effects caused by dextral shear in the central Shanxi rift. A comparison between predicted seismicity and historical earthquake records reveals some remarkable seismic gaps, particularly in the Datong, Hancheng, and Yuncheng basins, indicating higher seismic potential in these locations. This study provides insights into the long-term crustal deformation processes and regional seismic potential of the FWRZ.

A robust estimation algorithm for the increasing breakdown point based on quasi-accurate detection and its application to parameter estimation of the GNSS crustal deformation model

A robust estimation algorithm for the increasing breakdown point based on quasi-accurate detection and its application to parameter estimation of the GNSS crustal deformation model

Difference of shortening strain for the crustal deformation model in the eastern and western Qaidam Basin and their implications, northern Tibetan Plateau, China

To recognize the differences in the west–east crustal deformation model of the Qaidam Basin, we presented the shortening amount of each fold and fault along 12 sections. According to the eastward weakening trend of shortening strain in the southwestern part of the basin and the non‐continuous trend in the northeastern part of the basin, the Qaidam Basin can be divided by a new line into the western Qaidam Basin (WQB) and the eastern Qaidam Basin (EQB). The WQB is characterized by a maximum shortening strain of 25%, transpressional structures, and crust–mantle decoupling, which is possibly weakened by the eastward extension of the crust–mantle mix zone caused by upwelling material along the Altyn Tagh Fault (ATF). In contrast, the EQB is characterized by a minimum shortening strain of 2%, pure thrust boundary faults, and gentle folds, which is defined as a rigid craton basin. The crust–mantle mix zone beneath ATF and the low‐velocity zone beneath the eastern Kunlun Shan show the limited impact of the lithospheric weakening on the EQB. The Miocene reorganization of the ATF is the key tectonic event that accounts for the differences in the east–west crustal deformation model of the Qaidam Basin, as it weakened the lithosphere and facilitated the transpressional structures of the WQB. The WQB was originally a rigid craton basin like the EQB, but it became a destabilized craton after the a forementioned tectonic event.

Fault Displacement of the 2011 Mw 6.6 Fukushima-ken Hamadori Earthquake Based on a 3D Crustal Deformation Model Constructed Using Differential InSAR–Lidar

ABSTRACT 3D coseismic deformation detected by remote sensing yields essential information for estimating the geometry and slip distribution of the causative fault. However, it is often difficult to be obtained by a single observation method due to data acquisition constraints. This study constructs a 3D coseismic deformation model of the 2011 Fukushima-ken Hamadori earthquake by integrating Differential Interferometric Synthetic Aperture Radar (DInSAR), and differential light detection and ranging (Dlidar) analyses. Both horizontal and vertical movements observed are almost consistent with those of the theoretical dislocation model of normal faulting. The fault displacements measured within ±45 m of the rupture based on the 3D deformation model is also in good agreement with the possible maximum field displacements. Fault dips and lateral displacement components are also harmonious with the field survey measurements. Dlidar detects full 3D motion, whereas the DInSAR detects deformations too small for the light detection and ranging (lidar). Combining the two products is helpful to produce a more robust 3D displacement field than possible from the lidar alone.

Accretionary wedge and oceanic crust thickness effect on surface deformation: Study case the Mentawai segment

Southern Sumatra forearc is classified as a compressional accretionary type. The existence of the accretionary wedge has a significant role in sediment deformation. This sediment deformation may contribute to generating higher tsunami generation. A two-dimensional crustal deformation modeling was performed to analyze the influence of the accretionary wedge. Furthermore, oceanic crust thickness variations are also simulated in this modeling as the incoming plate’s role in surface deformation is poorly understood. The crustal deformation modeling consists of two types of earthquake period: interseismic period and coseismic period. Various geometry features were applied for each earthquake period. The crustal deformation modeling itself is based on the finite element method. The result shows that there are different effects on the geometrical model being used. The pattern and amount of surface deformation also depend on at which the fault is activated. Extended geometry models such as three-dimensional modeling will be required for further study.

Study on co-seismic energy losses from hypocenter to ocean bottom for Sumatra earthquake 2004 using 3-D crustal deformation model

Our co-seismic GRACE gravity data (Level 2 ‘RL_05’ data product “GX-OG-_2-GSM) for Sumatra earthquake 2004 is obtained by differencing monthly gravity field average for November 2004 from that of January 2005 and band-pass filtering (17–30, degrees and orders) in spectral domain. Here we propose an 11-layered 3-D thrust fault gravity model based on several co-seismic rupture models in literature. Previously we have covered the 3-D modelling details and its inferences like slip rate, seismic moment, momentum etc. in our published literature. Further we extend the inferences through our model for this case study. Here, we have estimated the layer-wise energy distribution by undertaking two types energy loss one is spherical spreading and second absorption with constrained by literature. We have computed layer-wise energy loss, equivalent energy, differential pressure, slip rate, ultimate slip and work done. The computed differential pressure and work done for Sumatra Earthquake 2004 are 1.7552 × 108 N/m2 and 1.657 × 1018 J, respectively. We also estimated the absorption coefficient (calculated absorption coefficients) from our model to honour the slip rate of Sumatra earthquake 2004. The differential pressure is estimated for ocean bottom and sea level surface. The volumetric analysis is also provided for entire 3-D body (layer-wise) using excess mass of our model. The computed differential pressure indeed corresponds to an area pulse at ocean bottom that led to a Tsunami generation.

Considering fault interaction in estimates of absolute stress along faults in the San Gorgonio Pass region, southern California

Abstract Present-day shear tractions along faults of the San Gorgonio Pass region (southern California, USA) can be estimated from stressing rates provided by three-dimensional forward crustal deformation models. Due to fault interaction within the model, dextral shear stressing rates on the San Andreas and San Jacinto faults differ from rates resolved from the regional loading. In particular, fault patches with similar orientations and depths on the two faults show different stressing rates. We estimate the present-day, evolved fault tractions along faults of the San Gorgonio Pass region using the time since last earthquake, fault stressing rates (which account for fault interaction), and coseismic models of the impact of recent nearby earthquakes. The evolved tractions differ significantly from the resolved regional tractions, with the largest dextral traction located within the restraining bend comprising the pass, which has not had recent earthquakes, rather than outside of the bend, which is more preferentially oriented under tectonic loading. Evolved fault tractions can provide more accurate initial conditions for dynamic rupture models within regions of complex fault geometry, such as the San Gorgonio Pass region. An analysis of the time needed to accumulate shear tractions that exceed typical earthquake stress drops shows that present-day tractions already exceed 3 MPa along portions of the Banning, Garnet Hill, and Mission Creek strands of the San Andreas fault. This result highlights areas that may be near failure if accumulated tractions equivalent to typical earthquake stress drops precipitate failure.

GPU-Accelerated Automatic Microseismic Monitoring Algorithm (GAMMA) and Its Application to the 2019 Ridgecrest Earthquake Sequence

Abstract Foreshocks and/or aftershocks play critical roles in improving our understanding of the processes of faulting, such as nucleation of earthquakes, earthquake triggering, and postseismic deformation. A rapid and accurate earthquake detection and location algorithm can provide timely information of seismic activities, thereby benefitting our understanding of physical mechanisms of faulting and seismic hazard assessment. We have developed a graphic processing unit (GPU)-accelerated automatic microseismic monitoring algorithm (GAMMA) for accurate and near real-time detection and location of earthquakes. GAMMA utilizes methods based on backprojection to automatically detect potential earthquakes, and then the waveforms of qualified earthquakes are selected as templates when searching for small earthquakes in continuous recordings using the template-matching algorithm. The use of GPUs has substantially accelerated the calculations and has made GAMMA capable of (near-)real-time earthquake monitoring. We have successfully applied GAMMA to the 2019 Ridgecrest earthquake sequence in southern California. The number of earthquakes detected by GAMMA is more than 21 times that documented in the regional catalog. The more complete catalog determined by GAMMA may provide crucial information for improving our understanding of the physical mechanisms of faulting and also supply useful constraints for a variety of types of studies, including dynamic rupture simulations and crustal deformation modeling.