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Comparison of forward-modeled maximum tsunami height between surface-rupturing (SR) and nonsurface-rupturing (NSR) scenarios. Predicted maximum tsunami height by NSR scenario, h max|NSR (Figure 4d) is subtracted by that of SR scenario, h max|NSR simulated in homogeneous (HOM; Figure 4a) and heterogeneous (HET). This yields prediction difference, Δh max|NSR-SR = h max|NSR À h max|SR , in (a) HET and (c) HOM, and percentage difference (Δh max|NSR-SR /|h max|SR |) in (b) HET and (d) HOM. Linear profiles (left) of each subfigure refer to values at coastal checkpoints. Linear profiles (left) of each subfigure refer to values at coastal checkpoints.
Source publication
This study reveals how modeling configurations of forward and inverse analyses of coseismic deformation data influence the estimations of seismic and tsunami sources. We illuminate how the predictions of nearfield tsunami change when (1) a heterogeneous (HET) distribution of crustal material is introduced to the elastic dislocation model, and (2) t...
Contexts in source publication
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... from ~0.3 m near Vancouver Island to ~0.8-1.0 m near Oregon, providing different conditions for modeling wave dynamics (Figures 6a and 6c). As a result, the subsurface rupture overall encourages a larger coastal |h max | by ~0.13-0.20 m on average which is equivalent to ~24-43% of an SR case (Figures 7b and 7d). On the contrary, smaller maximum amplitudes (Δh max ~À1 m) are predicted by NSR scenario than the SR scenario along the coastal cities of Southern Oregon (e.g., Gold Beach) and Northern California (e.g., Eureka) (Figures 7a and 7c). ...
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... a result, the subsurface rupture overall encourages a larger coastal |h max | by ~0.13-0.20 m on average which is equivalent to ~24-43% of an SR case (Figures 7b and 7d). On the contrary, smaller maximum amplitudes (Δh max ~À1 m) are predicted by NSR scenario than the SR scenario along the coastal cities of Southern Oregon (e.g., Gold Beach) and Northern California (e.g., Eureka) (Figures 7a and 7c). ...
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... mean of predicted coastal d z (~0.14 m in Figure 9c) deviates significantly from the actual values (~0.19 m in (Figures 11c, 12c, and S5c). The arrival of h max is largely coherent with the synthetic model ( Figure S7c). Furthermore, we also directly compare the solutions of HET_OPEN (Figure 8b) and HOM_OPEN (Figure 8d). ...
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... near-field tsunami hazards, the NSR mechanism usually creates more coast uplift by ~0.1 m (~20%) than the SR slips ( Figure 6). Their estimated h max could differ by up to 1.6 m (~130%) (Figures 7a and 7b). As expected by Satake et al. (2013), the h max of the NSR scenario arrives ~10 min earlier than that of the SR sce- nario ( Figure S2a). ...
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... with the solu- tions of other inversion schemes (Figures 12a-12c), HOM_CLOSED creates significantly more uncertainties (up to 3.7 m) of the predicted h max both onshore and offshore (Figure 12d). In this case, the worst predictions of d z (Figure 10d), h max (Figure 12d), and t hmax ( Figure S7d) are observed. In a forecasting prospective, we directly compare the solutions of HET_OPEN against HOM_CLOSED for the SR scenario (Figures 13e and 13f, 14e and 14f, and 15e and 15f) and those of HET_CLOSED against HOM_OPEN for the NSR scenario (Figures 13k and 13l, 14k and 14l, and 15k and 15l). ...
Citations
... Previous studies have contributed to the advancement of slip models in a 3D Earth structure (e.g., Wald and Graves, 2001;Williams and Wallace, 2015;Tung and Masterlark, 2018) and show that material contrasts between continental crust and oceanic slabs have a large effect on recovering static coseismic displacements, slow slip events, slip distributions and tsunami behavior in elastic models. For example, Tung and Masterlark (2018) show that the inclusion of heterogenous crustal structure can remove nonrealistic slip artifacts in slip distributions and reduce the misfit in large seafloor displacement that contributes to prediction error of tsunami amplitudes. ...
... Previous studies have contributed to the advancement of slip models in a 3D Earth structure (e.g., Wald and Graves, 2001;Williams and Wallace, 2015;Tung and Masterlark, 2018) and show that material contrasts between continental crust and oceanic slabs have a large effect on recovering static coseismic displacements, slow slip events, slip distributions and tsunami behavior in elastic models. For example, Tung and Masterlark (2018) show that the inclusion of heterogenous crustal structure can remove nonrealistic slip artifacts in slip distributions and reduce the misfit in large seafloor displacement that contributes to prediction error of tsunami amplitudes. Williams and Wallace (2015) also show a better fit to the observed GNSS displacements by computing Green's functions using a realistically varying elastic properties with a finite element method (Aagaard et al., 2013). ...
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.
... The left-bottom inlet shows the location of the proximal major faults, namely, the San Andreas Fault and Garlock Fault as well as the Eastern California shear zone and nearby significant events over the past decades. Tung, Fielding, et al., 2019;Tung, Katzenstein, et al., 2019;, 2018b2018c;Tung, Masterlark, & Lo, 2018;Williams & Wallace, 2015). In addition to modeling the fault kinematics, the nearfault elastic variabilities should also be considered for accurately calculating the geodetic slip moment (and moment magnitude) and Coulomb stress changes (Das et al., 2019;King et al., 1994;Langenbruch & Shapiro, 2014;Tung, Fielding, et al., 2019;Tung, Katzenstein, et al., 2019). ...
We develop finite element models of the coseismic displacement field accounting for the 3D elastic structures surrounding the epicentral area of the 2019 Ridgecrest earthquake sequence containing two major events of Mw7.1 and Mw6.4. The coseismic slip distribution is inferred from the surface displacement field recorded by interferometric synthetic aperture radar. The rupture dip geometry is further optimized using a novel nonlinear‐crossover‐linear inversion approach. It is found that accounting for elastic heterogeneity and fault along‐strike curvilinearity improves the fit to the observed displacement field and yields a more accurate estimate of geodetic moment and Coulomb stress changes. We observe spatial correlations among the locations of aftershocks and patches of high slip, and rock anomalous elastic properties, suggesting that the shallow crust's elastic structures possibly controlled the Ridgecrest earthquake sequence. Most of the coseismic slip with a peak slip of 7.4 m at 3.6 km depth occurred above a zone of reduced S‐wave velocity and significant post‐Mw7.1 afterslip. This implies that viscous materials or fluid presence might have contributed to the low rupture velocity of the mainshock. Moreover, the zone of high slip on the northwest‐trending fault segment is laterally bounded by two aftershock clusters, whose location is characterized by intermediate rock rigidity. Notably, some minor orthogonal faults consistently end above a subsurface rigid body. Overall, these observations of structural controls improve our understandings of the seismogenesis within incipient fault systems.
... 4-7) highlights individual structures and portions of the outer wedge that may focus strain accumulation and release, which is of great importance for charac terizing tsunami hazards associated with large offshore earthquakes. Accurate modeling of tsu namis and their impacts from local earthquakes (rather than distant sources) is dependent primarily on rupture details (Geist and Yoshioka, 1996;Wang and Tréhu, 2016) and the heterogeneity of crustal materials (Tung and Masterlark, 2018). The tsunami wave amplitude and waveform have the greatest influence on the tsunami runup at the coastline (Geist and Yoshioka, 1996). ...
Studies of recent destructive megathrust earthquakes and tsunamis along subduction margins in Japan, Sumatra, and Chile have linked forearc morphology and structure to megathrust behavior. This connection is based on the idea that spatial variations in the frictional behavior of the mega thrust influence the tectono-morphological evolution of the upper plate. Here we present a comprehensive examination of the tectonic geomorphology, outer wedge taper, and structural vergence along the marine forearc of the Cascadia subduction zone (offshore northwestern North America). The goal is to better understand geologic controls on outer wedge strength and segmentation at spatial scales equivalent to rupture lengths of large earthquakes (≥M 6.7), and to examine potential linkages with shallow megathrust behavior. We use cross-margin profiles, spaced 25 km apart, to characterize along-strike variation in outer wedge width, steepness, and structural vergence (measured between the toe and the outer arc high). The width of the outer wedge varies between 17 and 93 km, and the steepness ranges from 0.9° to 6.5°. Hierarchical cluster analysis of outer wedge width and steepness reveals four distinct regions that also display unique patterns of structural ver-gence and shape of the wedge: Vancouver Island, British Columbia, Canada (average width, linear wedge, seaward and mixed vergence); Washington, USA (higher width, concave wedge, landward and mixed vergence); northern and central Oregon, USA (average width, linear and convex wedge, mixed and seaward vergence); and southern Oregon and northern California, USA (lower width, convex wedge, seaward and mixed vergence). Variability in outer wedge morphology and structure is broadly associated with along-strike megathrust segmentation inferred from differences in oceanic asthenospheric velocities, patterns of episodic tremor and slow slip, GPS models of plate locking, and the distribution of seismicity near the plate interface. In more detail, our results appear to delin-eate the extent, geometry, and lithology of dynamic and static backstops along the margin. Varying backstop configurations along the Cascadia margin are interpreted to represent material-strength contrasts within the wedge that appear to regulate the along-and across-strike taper and structural vergence in the outer wedge. We argue that the morphotectonic variability in the outer wedge may reflect spatial variations in shallow mega-thrust behavior occurring over roughly the last few million years. Comparing outer wedge taper along the Cascadia margin to a global compilation suggests that observations in the global catalog are not accurately representing the range of hetero-geneity within individual margins and highlights the need for detailed margin-wide morphotectonic analyses of subduction zones worldwide.
... During the PE, an earthquake early warning system in Central Mexico successfully delivered prompt notifications to the public regarding the arrivals of vigorous strong motions (Jacobson & Stein, 2018). The success of this warning demonstrates the potentials for expanded warning systems to rapidly characterize slip distributions, aftershock, and tsunami hazards (Minson et al., 2014;Newman et al., 2011;Tung & Masterlark, 2018a, 2018cTung, Masterlark, and Dovovan, 2018). In the past, the real-time inversion for finite-fault models has been carried out with high-rate GPS data (Allen & Ziv, 2011;Colombelli et al., 2013;Crowell et al., 2012;Grapenthin et al., 2014;Li et al., 2013;Minson et al., 2014) and seismic wave data (Hayes, 2011;Hayes et al., 2015;Hsieh et al., 2016;Newman et al., 2011;Ross & Ben-Zion, 2016). ...
... The reliability of interpreting earthquake displacements largely depends on how well the elastic models simulate the lithospheric environments near the epicenter (Hearn & Bürgmann, 2005;Masterlark & Hughes, 2008;Moreno et al., 2009;Okada, 1985;Trasatti et al., 2011). Tung and Masterlark (2018c) discover significantly better recovery of coseismic displacements, earthquake sources, and tsunami behaviors when the elastic models account for the distinctive material contrast between the weaker continental crust and stiffer oceanic slab along the Cascadia subduction zone. This solution sensitivity toward material heterogeneity is also shown in other earthquake settings (e.g., Hikurangi margin; Hearn & Bürgmann, 2005;Williams & Wallace, 2015). ...
... Finite element models (FEMs) are well suited to simulate both of the above tectonic complexities (Hughes et al., 2010;Kyriakopoulos et al., 2013;Figure 2) and assimilate existing crustal information such as CRUST2.0 that cannot be well accommodated by rectangular fault patches in an analytical half-space (Okada, 1985). The advantages of using FEMs over customary half-space solutions have been exemplified in recent earthquakes and volcanic eruptions (Hughes et al., 2010;Kyriakopoulos et al., 2013;Masterlark, 2003;Masterlark et al., 2012;Masterlark et al., 2016;Masterlark & Hughes, 2008;Trasatti et al., 2011;, 2018b, 2018cWilliams & Wallace, 2015), contributing to significantly more accurate source information. Yet, the lengthy processes of building FEMs and the corresponding Green's function (GF) matrix are the bottlenecks of realtime analyses (c.f. ...
Plain Language Summary
A Mw7.2 earthquake took place near the city of Pinotepa Nacinoal in Oaxaca, Mexico, on 16 February 2018 and became the third most significant event striking southern Mexico since mid‐2017, after the Mw8.2 Tehuantepec and Mw7.1 Puebla‐Morelos earthquakes. A new algorithm of deformation modeling is designed to use a fault library to efficiently characterize the earthquake source. This library accounts for fault slip within both rock and structural complexities documented within the Middle America subduction zone. We further study 100 Mw8.6 megathrust scenarios and discover that an elastic model of these complexities is necessary to better recover the slip and surface displacements than the customary layered or uniform‐crust solutions. These Mw8.6 scenarios are the largest expected events based on historical records. Our algorithm images the Pinotepa earthquake rupture 18 min after the ground displacement data are downlinked from the satellite and processed in local machines, providing an alternative of evaluating the earthquake mechanism in addition to other seismological methods. The majority of fault slip (up to 1.2 m) is located over a gently dipping slab segment at a depth of ~21 km. These results illuminate the effectiveness and applicability of the proposed algorithm for real‐time analyses, without compromising model accuracy to analytical solutions.
... Here, we want to highlight the uncertainties on numerical modeling initial conditions and setup to estimate the five IMs. The MHW level was considered as the reference level, and even though the impacts of subsidence were considered in the ComMIT/MOST propagation simulation, the study included the impact of subsidence in the adjustment of the topographic conditions when analyzing the refined response using Coulwave (e.g., Adams et al. 2015;Tung and Masterlark 2018). Both the reference tide level and subsidence could result in significant differences on IMs related to inundation depth, but T A than T D results presented are less sensitive to. ...
Probabilistic Tsunami Hazard Analysis (PTHA) can be used to evaluate and quantify tsunami hazards for planning of integrated community-level preparedness, including mitigation of casualties and dollar losses, and to study resilient solutions for coastal communities. PTHA can provide several outputs such as the intensity measures (IMs) of the hazard quantified as a function of the recurrence interval of a tsunami event. In this paper, PTHA is developed using a logic tree approach based on numerical modeling for tsunami generated along the Cascadia Subduction Zone. The PTHA is applied to a community on the US Pacific Northwest Coast located in Newport, Oregon. Results of the PTHA are provided for five IMs: inundation depth, flow speed, specific momentum flux, arrival time, and duration of inundation. The first three IMs are predictors of tsunami impact on the natural and built environment, and the last two are useful for tsunami evacuation and immediate response planning. Results for the five IMs are presented as annual exceedance probability for sites within the community along several transects with varying bathymetric and topographic features. Community-level characteristics of spatial distribution of each IM for three recurrence intervals (500, 1000, 2500 year) are provided. Results highlight the different pattern of IMs between land and river transects, and significant magnitude variation of IMs due to complex bathymetry and topographic conditions at the various recurrence intervals. IMs show relatively higher magnitudes near the coastline, at the low elevation regions, and at the harbor channel. In addition, results indicate a positive correlation between inundation depth and other IMs near the coastline, but a weaker correlation at inland locations. Values of the Froude number ranged 0.1–1.0 over the inland inundation area. In general, the results in this study highlight the spatial differences in IMs and suggest the need to include multiple IMs for resilience planning for a coastal community subjected to tsunami hazards.
... Matsuyama et al. [65] underlines the importance of including non-uniform topography and bathometry in fault deformation model to assess the tsunami hazard and coastal impact upon tsunamigenic events. Subjected to the ongoing tectonic movements and irregular structural settings, seismogenic/tsunamigenic zones usually attain a variable topography or bathymetry, which can be well accommodated by our FEMs for better accuracy of source characterization and tsunami wave predictions ( Figure 1) [3,66]. ...
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 1D and 3D synthetic, 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 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.
The 2017 Mw 6.5 Jiuzhaigou earthquake (JE) struck a rugged area of the Jiuzhaigou Valley in eastern Tibet that has experienced frequent seismic activity over the last few decades. We use finite‐element models (FEMs) and Sentinel‐1 Interferometric Synthetic Aperture Radar observations to characterize the earthquake source. The FEM domain accommodates a heterogeneous (HET) distribution of realistic crustal materials inferred by regional seismic tomography data. The HET‐derived source configurations yield a significantly smaller misfit, at the 95% confidence level, than that estimated for a homogeneous (HOM) half‐space. The former generally requires a lower degree of smoothing constraint, highlighting that the HET solutions are systematically more compatible with the surface observations than the HOM solutions. The magnitudes of induced Coulomb failure stress change (ΔCFS) estimated by the HET solution drastically differ (by >0.1 MPa) from those calculated by the HOM solution. The postearthquake stability of near‐field faults is generally overestimated by the HOM estimations, whereas some localities of negative ΔCFSHOM are predicted with positive ΔCFSHET. These results highlight the sensitivities of both slip and stress estimations to the complexity of the adopted elastic modeling domain, leading to more accurate aftershock hazard assessments. The HET‐resolved seismic rupture reveals two major slip asperities of magnitude up to 0.83 m distributed along the fault strike, which is coherent with the aftershock distribution. Two aftershock clusters are consistently found near or below these two peak‐slip zones, which are imaged by the HET model but absent in the HOM solution. The JE hypocenter and aftershocks are bounded below by a negative velocity anomaly (ΔVP, ΔVS down to −4%) at ∼18 km depth. Such low‐velocity layers of reduced strength may be relevant to the vertical distribution of seismicity and earthquake slip, which provide insights into assessing the seismic hazards and aftershock‐prone areas of the eastern Tibetan margin.
