ORCID Profile
0000-0002-8768-2782
Current Organisations
Australian National University
,
Harvard University
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Seismology and Seismic Exploration | Hydrogeology | Geophysics |
Expanding Knowledge in the Earth Sciences | Environmental Management Systems | Rural Water Evaluation (incl. Water Quality)
Publisher: Seismological Society of America (SSA)
Date: 08-08-2018
DOI: 10.1785/0220180074
Publisher: Oxford University Press (OUP)
Date: 05-10-2020
DOI: 10.1093/GJI/GGAA472
Abstract: A teleseismic receiver function image of a slab-like feature that extends from the Pacific coast to the foothills of the Sierra Nevada beneath central California connects the expected location of the subducted remnant of the Monterey microplate to the high-velocity Isabella anomaly in the upper mantle. The observed structure indicates that this anomaly is a relic of the subduction zone that preceded capture of the Monterey microplate by the Pacific plate and is not due to the delamination of the lithosphere beneath the Sierra Nevada Mountains, as had been previously proposed. The fossil slab connection is also supported by surface wave tomographic images. The images are derived in part from a new linear broad-band array across the western part of central California.
Publisher: American Geophysical Union (AGU)
Date: 07-2020
DOI: 10.1029/2020TC006140
Publisher: McGill University Library and Archives
Date: 18-09-2023
Publisher: Elsevier BV
Date: 10-2019
Publisher: American Geophysical Union (AGU)
Date: 10-10-2018
DOI: 10.1029/2018GL079406
Abstract: Mantle shear velocity (Vs) structure beneath the Transportable Array (TA) in Alaska and northwestern Canada is imaged by joint inversion of Rayleigh wave dispersion and teleseismic S wave travel times. The study connects previously uns led parts of northern and western Alaska with portions of southern Alaska imaged with earlier seismic arrays. The new Vs tomography shows contrasting lithospheric structure in the plate interior with lower Vs shallow upper mantle indicative of thinner thermal lithosphere south of the Brooks Range and along the transform margin. Higher Vs down to ~200 km beneath the Brooks Range and northern coast is consistent with the presence of a cold stable lithospheric root that may help guide intraplate deformation to the south. In the subduction‐to‐transform transition, a potential slab fragment is imaged beneath the Wrangell volcanic field where modern subduction has slowed due to the thick buoyant crust of the Yakutat terrane.
Publisher: Elsevier BV
Date: 03-2015
Publisher: Wiley
Date: 19-10-2022
Publisher: American Geophysical Union (AGU)
Date: 06-2021
DOI: 10.1029/2021JB021648
Abstract: Adjoint tomography has been recently applied to ambient seismic noise and teleseismic P waves separately to unveil fine‐scale lithospheric structures beyond the resolving ability of traditional ray‐based traveltime tomography. In this study, we propose an inversion scheme that alternates between frequency‐dependent traveltime inversions of ambient noise surface waves and waveform inversions of teleseismic P waves to take advantage of their complementary sensitivities to the Earth's structure. We apply our method to ambient noise empirical Green's functions from 60 virtual sources, direct P and scattered waves from 11 teleseismic events recorded by a dense linear array (∼7 km station spacing) and other regional stations (∼40 km average station spacing) in central California. To evaluate the performance of the method, we compare tomographic results from ambient noise adjoint tomography, full‐waveform inversion of teleseismic P waves, and the alternating inversion of the two data sets. Both applications to practical field data sets and synthetic checkerboard tests demonstrate the advantage of the alternating inversion over in idual inversions as it combines the complementary sensitivities of the two independent data sets toward a more unified model. The three dimensional model from our alternating inversion not only shows major features of velocity anomalies and discontinuities in agreement with previous studies, but also reveals small‐scale heterogeneities which provide new constraints on the geometry of the Isabella Anomaly and mantle dynamic processes in central California. The proposed alternating inversion scheme can be applied to other regions with similar array deployments for high‐resolution lithospheric imaging.
Publisher: Wiley
Date: 24-02-2020
Publisher: Elsevier BV
Date: 06-2016
Publisher: Oxford University Press (OUP)
Date: 28-03-2016
DOI: 10.1093/GJI/GGW096
Publisher: American Geophysical Union (AGU)
Date: 08-2022
DOI: 10.1029/2022JB024613
Abstract: Metropolitan Tokyo is subject to significant seismic hazards because it is located near a triple junction of tectonic plates and because it sits atop the soft and thick sediments of the Kanto sedimentary Basin. Numerical simulations of earthquake ground motions rely on accurate velocity models of the basin elastic and anelastic structure, which remains to be improved. Here, we leverage the density of permanent stations of the Metropolitan Seismic Observation network seismic network to construct a high‐resolution radially anisotropic ( V SV ≠ V SH ) shear wave velocity model of the Kanto basin. We construct surface waves using ambient seismic noise cross correlations. In sedimentary structures, it is common for several surface‐wave modes to arise and to couple in time, so we use local sub‐arrays to extract the phase velocity of the fundamental mode and first overtone of Rayleigh and Love waves at short periods (1–7 s). We find that a strong and negative shear‐wave anisotropy (−5%) is confined to the upper 300 m depth range, and a strong and positive anisotropy (+5%) at greater depths. We interpret them as a result of the vertical cracks from repeated earthquake damage and sediment stratigraphy in the Kanto Basin. Because anisotropy models are not routinely used in physics‐based ground motion prediction, our study motivates the consideration of seismic anisotropy in sedimentary basins for the ground motion of future earthquakes.
Publisher: Oxford University Press (OUP)
Date: 12-04-2022
DOI: 10.1093/GJI/GGAC101
Abstract: Sedimentary basins can strongly lify seismic waves from earthquakes. To better predict future ground motions, detailed knowledge of the sediment thickness and internal structure of basins is required. We image the sediment-to-bedrock interface of the Kanto Basin in Japan using the P-wave reflectivity response from earthquake and ambient seismic noise autocorrelation functions (ACFs) at 286 shallow borehole stations. Earthquake ACFs are computed using P-wave records from 50 Mw 6+ teleseismic events. Noise ACFs are obtained using 1 month of continuous data. Both methods are used to retrieve P-wave traveltimes between the surface and the bedrock interface and map the basin basement geometry. Our prediction of the basement depth agrees generally well with that from a reference velocity model, except for smoother variations in the central part of the basin. Using full-wavefield simulations, we show that the nature of the autocorrelated wavefield has a significant impact on the shape of the ACF waveforms and that earthquake ACFs yield more accurate results in the Kanto Basin.
Publisher: Informa UK Limited
Date: 15-06-2023
Publisher: American Geophysical Union (AGU)
Date: 07-2023
DOI: 10.1029/2022JB026162
Abstract: Since the continental collision between the Indian and Eurasian plates began about 50 Ma ago, southeastern Tibet (SET) has undergone complex tectonic deformation. In this study, we investigate fine scale structural features of the crustal and upper mantle depths ( km) beneath SET, which hold important clues to understanding the dynamic processes related to this collision. A 3D shear velocity model is constructed through jointly inverting Rayleigh wave phase velocity and teleseismic body wave data from more than 650 stations. Our 3D model identifies three independent low‐velocity zones (LVZs) in the mid‐lower crust with unprecedented details. More specifically, we observe a prominent LVZ beneath the North Chuan‐Dian Block, which is well separated from another LVZ beneath the Tengchong volcano in the south. This LVZ beneath the volcano represents a focused magma reservoir in the crust whose origin is potentially linked to the mantle upwelling associated with the eastward subduction of the Indian plate. The third LVZ, observed around the Xiaojiang Fault, likely represents a separated and mechanically weak layer in the mid‐lower crust due to the combined effects of regional crustal thickening under the southeastward plateau expansion, mantle upwelling, and shear heating of strike‐slip faults. In the upper mantle, we observe strong velocity reductions both in localized areas beneath the Tibetan Plateau and the broad region south of 26°N. These low velocity anomalies are sitting above high velocity anomalies at deeper depths, suggesting their association with lithospheric thickening and delamination processes.
Publisher: American Geophysical Union (AGU)
Date: 08-2022
DOI: 10.1029/2022GC010446
Abstract: Surface wave tomography is widely used to improve our understanding of continental magma reservoirs that may be capable of fueling explosive volcanic eruptions. However, traditional surface wave tomography based on inversions for phase velocity maps and locally 1D shear velocity may have difficulty resolving strong 3D low‐velocity anomalies associated with crustal magma reservoirs. Here, we perform synthetic tomography experiments based on 3D seismic waveform simulations to understand how the limitations of surface wave tomography could affect interpretations of tomography in volcanic settings. We focus our modeling on the Yellowstone volcanic system, one of the largest and most thoroughly studied continental magmatic systems, and explore scenarios in which the maximum shear velocity anomaly associated with the crustal magma reservoir ranges between −10% and −66%. We find that even with the well‐instrumented setting near Yellowstone, the recovered shear velocity anomalies in the mid‐to‐upper crust are severely diminished due to the small spatial scale of the reservoir with respect to the seismic wavelengths that s le it. In particular, recovered V S anomalies could be reduced by a factor of two or more, implying that the inferred melt fraction of large‐scale continental magma reservoirs may be considerably underestimated.
Publisher: Wiley
Date: 08-10-2022
Publisher: American Geophysical Union (AGU)
Date: 06-03-2023
DOI: 10.1029/2022GL101520
Abstract: Valles Caldera was formed by large rhyolitic eruptions at ∼1.6 and 1.23 Ma and it hosts post‐caldera rhyolitic deposits as young as ∼69 ka, but the contemporary state of the magmatic system is unclear. Local seismicity beneath Valles Caldera is rare and shear‐velocity (Vs) structure has not been previously imaged. Here, we present the first local Vs tomography beneath Valles Caldera using ambient noise Rayleigh dispersion from a ∼71 km transect of nodal seismographs with mean spacing of ∼750 m. An ∼6 km wide low‐Vs anomaly (Vs 2.1 km/s) is located at ∼3–10 km depth within the 1.23 Ma caldera's ring fracture. Assuming magma in textural equilibrium, the new tomography suggests that melt fractions up to ∼17%–22% may be present within the upper crustal depth range where previously erupted rhyolites were stored.
Publisher: Elsevier BV
Date: 04-2018
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 05-2011
Publisher: Geological Society of America
Date: 12-07-2018
DOI: 10.1130/G45104.1
Publisher: American Geophysical Union (AGU)
Date: 12-08-2022
DOI: 10.1029/2022GL100233
Abstract: We present a high‐resolution P ‐wave azimuthally anisotropic velocity model for the upper and middle crust beneath southern California by a novel adjoint‐state traveltime tomography technique. Our model reveals significant anisotropy variations between tectonic blocks that clearly reflect both past and current plate boundary deformation. In the shallow crust, seismic anisotropy is mostly controlled by the preferred alignment of microcracks related to the present N‐S compressive stress while at deeper depths ( ∼6 km), seismic anisotropy mainly records paleofabrics formed during the long‐lived Farallon subduction and later extension that have not been fully reset by the present transform motion. Interestingly, our model demonstrates distinct fast axes beneath the western Transverse Ranges from its neighboring blocks, probably reflecting the large‐scale vertical axis clockwise rotation of the block. In addition, we identify layered structures with distinct anisotropy features beneath the Salton Trough, which could be a result of the current transtension.
Publisher: American Geophysical Union (AGU)
Date: 15-06-2020
DOI: 10.1029/2020GL088580
Abstract: We build a new radially anisotropic shear wave velocity model of Southern California based on ambient noise adjoint tomography to investigate crustal deformation associated with Cenozoic evolution of the Pacific‐North American plate boundary. Pervasive positive radial anisotropy (4%) is observed in the crust east of the San Andreas Fault (SAF), attributed to subhorizontal alignment of mica/ hibole foliation planes resulting from significant crustal extension. Substantial negative anisotropy (6%) is revealed in the middle/lower crust west of the SAF, where high shear wave speeds are also observed. The negative anisotropy could result from steeply dipping hibole schists in a shear zone developed during Laramide flat slab subduction. Alternatively, it could be caused by the crystal preferred orientation (CPO) of plagioclase, whose fast axis aligns orthogonally to a presumed subhorizontal foliation. The latter new mechanism highlights potentially complex CPO patterns resulting from different lithospheric mineralogy, as suggested by laboratory experiments on xenoliths from the region.
Publisher: Wiley
Date: 21-10-2020
Publisher: Seismological Society of America (SSA)
Date: 04-2020
DOI: 10.1785/0220190364
Abstract: The fast-growing interests in high spatial resolution of seismic imaging and high temporal resolution of seismic monitoring pose great challenges for fast, efficient, and stable data processing in ambient-noise seismology. This coincides with the explosion of available seismic data in the last few years. However, the current computational landscape of ambient seismic field seismology remains highly heterogeneous, with in idual researchers building their own homegrown codes. Here, we present NoisePy—a new high-performance python tool designed specifically for large-scale ambient-noise seismology. NoisePy provides most of the processing techniques for the ambient field data and the correlations found in the literature, along with parallel download routines, dispersion analysis, and monitoring functions. NoisePy takes advantage of adaptable seismic data format, a parallel input and output enabled HDF5 data format designed for seismology, for a structured organization of the cross-correlation data. The parallel computing of NoisePy is performed using Message Passing Interface and shows a strong scaling with the number of cores, which is well suited for embarrassingly parallel problems. NoisePy also uses a small memory overhead and stable memory usage. Benchmark comparisons with the latest version of MSNoise demonstrate about four-time improvement in compute time of the cross correlations, which is the slowest step of ambient-noise seismology. NoisePy is suitable for ambient-noise seismology of various data sizes, and it has been tested successfully at handling data of size ranging from a few GBs to several tens of TBs.
Publisher: Elsevier BV
Date: 02-2013
Publisher: Seismological Society of America (SSA)
Date: 2022
DOI: 10.1785/0320210041
Abstract: The tectonic setting of Timor–Leste and Eastern Indonesia comprises of a complex transition from oceanic lithosphere subduction to arc-continental collision. To better understand the deformation and convergent-zone structure of the region, we derive a new catalog of earthquake hypocenters and magnitudes from a temporary deployment of five years of continuous seismic data using an automated processing procedure. This includes a machine-learning phase picker, EQTransformer, and a sequential earthquake association and location workflow. We detect and locate ∼19,000 events during 2014–2018, which demonstrates that it is possible to characterize earthquake sequences from raw seismic data using a well-trained machine-learning picker for a complex convergent plate setting. This study provides the most complete catalog available for the region for the duration of the temporary deployment, which includes a complex pattern of crustal events across the collision zone and into the back-arc, as well as abundant deep slab seismicity.
Publisher: Elsevier BV
Date: 11-2014
Publisher: American Geophysical Union (AGU)
Date: 03-2023
DOI: 10.1029/2022GC010738
Abstract: Volcanic arcs consist of many distinct vents that are ultimately fueled by the common melting processes in the subduction zone mantle wedge. Seismic imaging of crustal‐scale magmatic systems can provide insight into how melt is organized in the deep crust and eventually focused beneath distinct vents as it ascends and evolves. Here, we investigate the crustal‐scale structure beneath a section of the Cascades arc spanning four major stratovolcanoes: Mt. Hood, Mt. St. Helens (MSH), Mt. Adams (MA), and Mt. Rainier, based on ambient noise data from 234 seismographs. Simultaneous inversion of Rayleigh and Love wave dispersion constrains the isotropic shear velocity ( Vs ) and identifies radially anisotropic structures. Isotropic Vs shows two sub‐parallel low‐ Vs zones (∼3.45–3.55 km/s) at ∼15–30 km depth with one connecting Mt. Rainier to MA, and another connecting MSH to Mt. Hood, which are interpreted as deep crustal magma reservoirs containing up to ∼2.5%–6% melt, assuming near‐equilibrium melt geometry. Negative radial anisotropy, from vertical fractures like dikes, is prevalent in this part of the Cascadia, but is interrupted by positive radial anisotropy, from subhorizontal features like sills, extending vertically beneath MA and Mt. Rainier at ∼10–30 km depth and weaker and west‐dipping positive anisotropy beneath MSH. The positive anisotropy regions are adjacent to rather than co‐located with the isotropic low‐ Vs anomalies. Ascending melt that stalled and mostly crystallized in sills with possible compositional differences from the country rock may explain the near‐average Vs and positive radial anisotropy adjacent to the active deep crustal magma reservoirs.
Publisher: American Geophysical Union (AGU)
Date: 09-05-2018
DOI: 10.1029/2018GL077476
Publisher: American Association for the Advancement of Science (AAAS)
Date: 02-12-2022
Abstract: Seismic tomography has provided key insight into Yellowstone’s crustal magmatic system that includes attempts to understand the melt distribution in the subsurface and the current stage of the volcano’s life cycle. We present new tomographic images of the shear wave speed of the Yellowstone magmatic system based on full waveform inversion of ambient noise correlations, which illuminates shear wave speed reductions of greater than 30% associated with Yellowstone’s silicic magma reservoir. The slowest seismic wave speeds (shear wave speed less than 2.3 kilometers per second) are present at depths between 3 and 8 kilometers, overlapping with petrological estimates of the assembly depth of erupted rhyolite bodies. Assuming that Yellowstone’s magmatic system is a crystal mush with broadly distributed melt, we estimate a partial melt fraction of 16 to 20%.
Publisher: Oxford University Press (OUP)
Date: 18-10-2022
DOI: 10.1093/GJI/GGAC410
Abstract: Cross-correlations of ambient seismic noise are widely used for seismic velocity imaging, monitoring and ground motion analyses. A typical step in analysing noise cross-correlation functions (NCFs) is stacking short-term NCFs over longer time periods to increase the signal quality. Spurious NCFs could contaminate the stack, degrade its quality and limit its use. Many methods have been developed to improve the stacking of coherent waveforms, including earthquake waveforms, receiver functions and NCFs. This study systematically evaluates and compares the performance of eight stacking methods, including arithmetic mean or linear stacking, robust stacking, selective stacking, cluster stacking, phase-weighted stacking, time–frequency phase-weighted stacking, Nth-root stacking and averaging after applying an adaptive covariance filter. Our results demonstrate that, in most cases, all methods can retrieve clear ballistic or first arrivals. However, they yield significant differences in preserving the phase and litude information. This study provides a practical guide for choosing the optimal stacking method for specific research applications in ambient noise seismology. We evaluate the performance using multiple onshore and offshore seismic arrays in the Pacific Northwest region. We compare these stacking methods for NCFs calculated from raw ambient noise (referred to as Raw NCFs) and from ambient noise normalized using a one-bit clipping time normalization method (referred to as One-bit NCFs). We evaluate six metrics, including signal-to-noise ratios, phase dispersion images, convergence rate, temporal changes in the ballistic and coda waves, relative litude decays with distance and computational time. We show that robust stacking is the best choice for all applications (velocity tomography, monitoring and attenuation studies) using Raw NCFs. For applications using One-bit NCFs, all methods but phase-weighted and Nth-root stacking are good choices for seismic velocity tomography. Linear, robust and selective stacking methods are all equally appropriate choices when using One-bit NCFs for monitoring applications. For applications relying on accurate relative litudes, the linear, robust, selective and cluster stacking methods all perform well with One-bit NCFs. The evaluations in this study can be generalized to a broad range of time-series analysis that utilizes data coherence to perform ensemble stacking. Another contribution of this study is the accompanying open-source software package, StackMaster, which can be used for general purposes of time-series stacking.
Start Date: 03-2022
End Date: 06-2025
Amount: $434,107.00
Funder: Australian Research Council
View Funded Activity