3D Seismic Model Research Articles

Double Seismic Zones along the Eastern Aleutian-Alaska Subduction Zone Revealed by a High-Precision Earthquake Relocation Catalog

Abstract The Eastern Aleutian-Alaska Subduction Zone (EAASZ) manifests significant along-strike variations in structure and geometry. The limited spatial resolution in intermediate-depth earthquake locations precludes investigation of small-scale variations in seismic characteristics. In this study, we use an existing 3D seismic velocity model and waveform cross-correlation data to relocate the earthquakes in 2016 near the EAASZ. Our improved absolute and relative earthquake locations reveal complex spatial characteristics of double seismic zones (DSZs). There are significant variations in location, depth, layer separation, and length of the DSZs along the EAASZ. We also observe nonuniform layer separations along the slope of the subducting slab that may imply either rheological or crustal thickness variations. In addition, our results suggest a triple seismic zone (TSZ) beneath Kenai. The interplay among different factors, including dehydration of metamorphic facies, intraslab stress, preexisting structures, and abrupt changes in slab geometry, may explain the observed variations in seismogenesis of the DSZs and TSZs. The comparison of our relocated seismicity with the thermal model for the slab beneath Cook Inlet shows that the intermediate-depth earthquakes occur between 500°C and 900°C isotherms. The 2016 Mw 7.1 Iniskin earthquake and its aftershocks are located at ∼800°C–900°C. The intricate small-scale variations in different characteristics of the DSZs and intermediate-depth seismicity and their correlations with major geometrical and physical controls can provide insight into what governs the seismogenesis of subduction-induced earthquakes.

3D outcrop geologic modeling and seismic forward modeling of mound-beach complexes

3D outcrop geologic modeling and seismic forward modeling of mound-beach complexes

Evaluation and Updates for the USGS San Francisco Bay Region 3D Seismic Velocity Model in the East and North Bay Portions

ABSTRACTWe update the eastern and the northern portions of the detailed domain of the U.S. Geological Survey San Francisco Bay region 3D seismic velocity model (SFVM) based on comparisons of recorded and synthetic ground motions from 20 moderate (Mw 3.7–4.6) earthquakes. We modify the current SFVM (v.08.3.0) by assigning alternate property-versus-depth relations to the existing 3D geologic model. In some places, changes correspond to reassigning correct relations in which geologic units appear to be mislabeled, and in other places we subdivide geologic units where mapped geologic boundaries are missing from the 3D models so that we can implement a velocity contrast across a boundary. We also make ad hoc adjustments to velocity rules near the surface in some areas to better fit arrival times (specifically, in the Livermore basin). The updates reduce misfits in waveform correlation, travel time, cumulative absolute displacement, and peak ground velocity and are included in v.21.1 of the model. The selected earthquakes are small enough so that we neglect finite-source effects and model them as point sources. This allows us to assume that observed waveform characteristics are the result of path effects, and discrepancies between synthetic and recorded motions arise from misrepresentation of the elastic properties. Our analysis suggests refining the 3D geologic model, and adjusting the rules assigning properties to the geologic units will further improve the accuracy of the SFVM for simulating earthquake ground motions.

Site parameters applied in NGA-Sub database

NGA-Sub data resources are organized into a relational database. We describe the Site table within that database structure, which contains metadata for 6502 stations that have recorded earthquakes incorporated into the database. Critical site parameters for ground motion modelling are time-averaged shear-wave velocity ( VS) in the upper 30 m of the site ( VS30) and depths to various VS horizons (1.0 and 2.5 km/s). We compile VS profiles for the global study regions and use these data to compute VS30 where profile data is available from reliable sources. When this is not the case, which is commonly encountered in many regions, we adopt a proxy-based VS30-estimation framework whereby estimates are provided, in order of preference, from locally derived models, models derived for a source region and applied to a different target region with some degree of validation, and global or source-region models applied to a target region without validation. Epistemic uncertainties in category median VS30 are provided when proxy-based models are required but their validation is not possible. Sediment depth terms are also evaluated using measured VS profiles that exceed measured velocity thresholds where available or are estimated for regions having 3D seismic velocity models (e.g. Cascadia, Japan, New Zealand, and Taiwan).

Constructing shear velocity models from surface wave dispersion curves using deep learning

Surface wave tomography has been widely used to determine shear wave velocities by inverting surface wave dispersion curves. Conventional least-squares inversions strongly depend on an initial model and Monte Carlo inversion algorithms are usually time-consuming. In this study, we apply a deep neural network (DNN) to surface wave dispersion curves to investigate whether the initial model can be relaxed and whether reliable shear velocity models can be constructed. By applying our method to synthetic and field data, our results show that: (1) by constructing a well-trained DNN model from the global continental CRUST1.0 data, the DNN approach is effective and efficient to determine shear velocity structures using Rayleigh wave dispersion curves; (2) using the well-trained DNN model, no prior model is required, relaxing the requirement of an initial model; (3) the well-trained DNN model can be used to construct pseudo 3D seismic models across different continental areas.

Three-Dimensional Seismic-Wave Propagation Simulations in the Southern Korean Peninsula Using Pseudodynamic Rupture Models

ABSTRACTAccurate and practical ground-motion predictions for potential large earthquakes are crucial for seismic hazard analysis of areas with insufficient instrumental data. Studies on historical earthquake records of the Korean Peninsula suggest that damaging earthquakes are possible in the southeastern region. Yet classical ground-motion prediction methods are limited in considering the physical rupture process and its effects on ground motion in complex velocity structures. In this study, we performed ground-motion simulations based on rigorous physics through pseudodynamic source modeling and wave propagation simulations in a 3D seismic velocity model. Ensembles of earthquake scenarios were generated by emulating the one- and two-point statistics of earthquake source parameters derived from a series of dynamic rupture models. The synthetic seismograms and the distributions of simulated peak ground velocities (PGVs) were compared with the observations of the 2016 Mw 5.4 Gyeongju earthquake in the Korean Peninsula. The effects of surface-wave radiation, rupture directivity, and both local and regional amplifications from the 3D wave propagation were reproduced accurately in the spatial distribution of simulated PGVs, in agreement with the observations from dense seismic networks by mean log residuals of −0.28 and standard deviations of 0.78. Amplifications in ground motions were found in regions having low crustal velocities and in regions of constructive interference from the crustal shear-wave phases associated with postcritical reflections from the Moho discontinuity. We extended the established approach to earthquake scenarios of Mw 6.0, 6.5, and 7.0, at the same location, to provide the distribution of ground motions from potential large earthquakes in the area. Although we demonstrate the value of these simulations, improvements in the accuracy of the 3D seismic velocity model and the scaling relationship of the source models would be necessary for a more accurate estimation of near-source ground motions.

3D seismic velocities modeling and its application in the appreciation of the complex deep framework; the Sisseb-El Alem basin, central-eastern Tunisia

3D seismic velocities modeling and its application in the appreciation of the complex deep framework; the Sisseb-El Alem basin, central-eastern Tunisia

USTClitho2.0: Updated Unified Seismic Tomography Models for Continental China Lithosphere from Joint Inversion of Body-Wave Arrival Times and Surface-Wave Dispersion Data

Abstract Xin et al. (2019) presented 3D seismic velocity models (VP and VS) of crust and uppermost mantle of continental China using seismic body-wave travel-time tomography, which are referred to as Unified Seismic Tomography Models for Continental China Lithosphere 1.0 (USTClitho1.0). Compared with previous models of continental China, the VP and VS models of USTClitho1.0 have the highest spatial resolution of 0.5°–1.0° in the horizontal direction and are useful for better understanding the complex tectonics of continental China. Although USTClitho1.0 is implicitly constrained by surface-wave data by using the VS model from surface-wave tomography and the converted VP model as initial models for body-wave travel-time tomography, the predicted surface-wave dispersion curves from USTClitho1.0 do not fit the observed data well. Here, we present updated 3D VP and VS models of the continental China lithosphere (USTClitho2.0) by joint inversion of body-wave arrival times and surface-wave dispersion data. Compared with the previous joint inversion scheme of Zhang et al. (2014), similar to Fang et al. (2016), it is further improved by including the sensitivity of surface-wave dispersion data to VP in the new joint inversion system. As a result, the shallow VP structure is also better imaged. In addition, the new joint inversion scheme considers the large topography variations between the eastern and western parts of China. Thus, USTClitho2.0 better resolves the upper-crustal structure of the Tibetan plateau. Compared with USTClitho1.0, USTClitho2.0 fits both body-wave arrival times and surface-wave dispersion data. Thus, the new velocity models are more accurate and can serve as a better reference model for regional-scale tomography and geodynamic studies in continental China.

Anelasticity and Lateral Heterogeneities in Earth's Upper Mantle: Impact on Surface Displacements, Self‐Attraction and Loading, and Ocean Tide Dynamics

AbstractSurface displacement and self‐attraction and loading (SAL) elevation induced by ocean tides are known to be affected by material properties of the solid Earth. Recent studies have shown that, in addition to elasticity, anelasticity considerably impacts surface displacements due to ocean tide loading (OTL). We employ consistent 3D seismic elastic and attenuation tomography models to construct 3D elastic and anelastic earth models, and derive corresponding averaged 1D elastic/anelastic models. We apply these models to systematically study the impact of anelasticity and lateral heterogeneity on M2 OTL displacements and SAL elevation. We find that neglecting lateral heterogeneities highly underestimates displacements and SAL elevation in mid‐ocean‐ridge regions and in some coastal areas of North and Central America. In comparison to PREM, 3D anelastic models can increase the predicted amplitudes of the vertical displacement and SAL elevation by up to 1.5 mm. The increased amplitudes reduce the discrepancy between GPS‐observed OTL displacements and their predictions based on PREM in places like Cornwall (England), Brittany (France), and the Ryukyu Islands (Japan). Applying our results to ocean tides, we discover that the impact on ocean tide dynamics exceeds the predicted SAL elevation correction with an RMS of about 1 mm, reaching an RMS of more than 5 mm in areas like North Atlantic or East Pacific. Due to the fact that such a value reaches the accuracy of modern data‐constrained tidal models, we regard the impact of anelastic shear relaxation as significant in tidal modeling.

Three-dimensional seismic performance analysis of large and complex underground pipe trench structure

The existed 1D (dimensional) and 2D seismic analysis methods couldn't met the seismic research requirements of large and complex underground pipe trench structure (LCUP). In order to solve the problem that the seismic performance analysis of LCUP requires high 3D modeling ability and calculation equipment, an integrated seismic analysis method of "overall structure + key nodes" was proposed in this paper. Firstly, according to the research purpose, the seismic analysis strategy of LCUP was proposed, and the main factors influencing the seismic time history analysis of LCUP were analyzed one by one, and a series of accurate analysis parameters and simplified assumptions were obtained. Secondly, the 3D seismic analysis model of LCUP was established, including the overall pipe trench model and the local key nodes model, and the material parameters, boundary conditions, ground motion and calculation conditions of the model were determined. Finally, 3D seismic time history analysis was carried out for the whole structure and key joints, and the seismic performance evaluation based on mechanics and deformation was carried out. The seismic performance of the LCUP met the design requirements. The results showed that the method didn't only meet the requirements of seismic analysis accuracy and depth for complex underground space structure, but also significantly reduced the time of seismic analysis and improves the research efficiency. This research method will provide a useful reference for the seismic research of similar large complex underground structures.

Shallow Magma Storage Beneath Mt. Etna: Evidence From New Attenuation Tomography and Existing Velocity Models

AbstractWe present a new three‐dimensional (3D) image of attenuation beneath Mt. Etna volcano based on the coda normalization method. Mt. Etna is an ideal natural laboratory for the application of new or unconventional tomography techniques owing to high levels of seismicity spanning a wide range of epicentral distances and depths. We retrieved seismic waveforms from the database generated in the 2014 TOMO‐ETNA seismic experiment and performed a joint interpretation of tomographic and geophysical inversion models to better constrain interpretations of the volcanic structure. We compared the attenuation tomography results with seismic inversion models (two P wave seismic models and a 3D coda wave seismic attenuation model) and the literature to highlight and interpret structural elements and their impact on the volcano dynamics. We created a new image of the inner structure of Mt. Etna that will help to constrain present and future volcanic behavior. In particular, we focused on magma storage below the summit area and identified a large high‐attenuation volume that is characterized by physical properties compatible with the presence of magma and other fluids. The existence of such a large volume of magma in the shallow crust below Mt. Etna has implications for the eruptive potential of the volcano.

Geological feature clarification of the contact zone of Akhskaya and Cherkashinskaya formations on the example of Priobskaya area

The first phase of subcycle AC12 formation on the example of the southern part of the Priobskoye field is considered. The job is done based on 3d seismic and geological model complexing with the using log interpretation. The erosion zone that violates the original structure of the upper part of the deep-sea clay pack III of akhskaya formation by paleochannels was revealed. These erosions form lithologic traps, isolated from the top productive reservoirs of subcycle AC12.

Applying an advanced temporal and spatial high-order finite-difference stencil to 3D seismic wave modeling

Present finite-difference (FD) algorithms for modeling seismic wave propagation in 3D acoustic media are mainly based on the traditional orthogonal stencil and can achieve spatial high-order but temporal second-order accuracy. Therefore, these approaches may result in visible temporal dispersion and even instability for relatively large time sampling intervals. In this paper, we develop an advanced FD stencil with temporal and spatial arbitrary even-order accuracy to solve the 3D acoustic wave equation. The temporal derivative is approximated by an octahedron stencil with the operator length N together with the traditional second-order FD. Meanwhile, the spatial derivatives are calculated by the orthogonal stencil with the operator length M. The plane-wave theory is introduced to derive the time-space-domain dispersion relation and estimate the corresponding high-order FD coefficients by Taylor expansion. To achieve higher accuracy, we further optimize FD coefficients by applying least-squares (LS) to minimize the relative error of the time-space-domain dispersion relation. Dispersion and stability analyses show that our new schemes have higher modeling accuracy and propagation stability than the conventional method. Numerical examples demonstrate that the proposed FDs can generate greater temporal accuracy on the prerequisite of preserving satisfactory spatial accuracy. Our new temporal high-order FD stencil by incorporating larger time step, shorter operator lengths, LS-based coefficients and variable-length operators can be regarded as a kind of accurate and efficient tool for seismic wave modeling.

New insights into the High Agri Valley deep structure revealed by magnetotelluric imaging and seismic tomography (Southern Apennine, Italy)

We present an electrical resistivity model obtained from a 2D Magnetotelluric survey across a large sector of the Southern Apennine in the High Agri Valley (HAV), a NW-SE trending intra-mountain basin, with a high seismogenic potential. The intensive hydrocarbon exploitation (Val d'Agri oilfield) makes this area also affected by induced seismicity. In this HAV sector, the injection of salt-water in an unproductive disposal well (Costa Molina 2) causes localized swarms of microearthquakes; a second cluster of continuous induced seismicity is also observed SW of the Pertusillo Lake and it is associated to the seasonal fluctuations of the reservoir's water level.The major insight inferred from this study concerns a better understanding of the geological and tectonic framework in the HAV. The electrical resistivity model images the subsurface as conductive sedimentary sequences (Allochthonous Units) upon the carbonate Apulian Platform Unit characterized by higher resistivity values. Both these units appear composed of thrust-and-fold system deepening with larger wavelength anticlines N-E toward. Most of the structures identified in the magnetotelluric model are rather superficial and confined within the Allochthonous Units. A sudden break of the Apulian platform under the central part of the MT profile defines a conductive zone possibly associated to a major SW-dipping reverse fault or to several branches, as closely spaced thrust-sheets cutting eastern flanks of the Agri Valley.Additional information on the HAV deep structures comes from the joint interpretation of the resistivity model and a 3D seismic tomographic model obtained from the inversion of passive seismic data collected in the period 2002–2018. The availability of this elastic representation of the subsurface allowed us to perform a cluster analysis on the electrical resistivity and seismic P-wave velocity distribution within the subsoil. This joint quantitative interpretation unveiled new insights, otherwise hidden by individual models, on the subsurface structure distinguishing some rheological zones in terms of barriers and asperities.

The missing craton edge: Crustal structure of the East European Craton beneath the Carpathian Orogen revealed by double-difference tomography

The Trans-European Suture Zone (TESZ) is the most important and extensive continental suture in Europe, marking the edge of the East European Craton (EEC), from the North Sea to the Black Sea. It corresponds to significant changes in surface geology and deep crustal structure, evident in seismic, gravitational and magnetic studies. However, the TESZ disappears beneath the Eastern Carpathians accretionary nappes and Neotethys ophiolites, thrusted over the subducted EEC passive margin in Romania that may have experienced progressive southward break-off generating post-collisional volcanism and anomalous seismicity in the Vrancea region of the South-East Carpathians. To illuminate the missing TESZ section and investigate the change in crustal properties from the Precambrian EEC across the collisional orogen and the impact of related volcanism, we determined a 3D seismic model of P and S wave velocities of the Eastern Carpathians in Romania. With the advent of new permanent broadband and short-period seismic stations of the Romanian Seismic Network, we were able to lower the earthquake magnitude detection threshold to 0.5 ML, largely expanding the earthquake database and create seismic images of the crust across the Carpathians. Using double-difference tomography and waveform cross-correlation differential times, we relocated local crustal earthquakes between 2010 and 2017 and jointly inverted for the 3D P and S -wave velocity structure down to the Moho discontinuity. Our study provides the highest resolution 3D crustal seismic model of this area to date and emphasizes the manifestation of surface tectonic boundaries at lower crustal depths. The TESZ is highlighted at mid-to lower-crustal depths beneath the Carpathian nappes, east of the post-collisional volcanic belt, as a gently-dipping transition from high Vp in the eastern footwall, the dipping Precambrian basement, to low Vp beneath the Carpathian Orogen to the west and a downward decrease in Vp/Vs. In parts of the volcanic region, Vp/Vs ratios increase suggesting the presence of fluids, mafic material and partial melts that may have altered the seismic structure of the TESZ. Relocated hypocenters are vertically distributed in the velocity transition zone from low to high especially beneath the youngest volcanoes in the south, consistent with a hypothetically active magmatic plumbing system. In the northern segment, where volcanoes are older, relatively high velocities are estimated and seismicity tends to cluster in the top 10 km, likely connected to a recently reactivated fault system. Seismicity in the foreland of the East Carpathians aligns along the NW-SE trending major crustal faults and continues beneath the thrust belt, suggesting the East European Craton basement extends beneath the orogen as far as the volcanic belt.

Seismic Analysis of the Reef-seawater System: Comparison between 3D and 2D Models

ABSTRACT This study established a 3D seismic analysis model for the reef-seawater system, in which the fluid-solid interaction algorithm, the fluid and solid artificial boundaries are adopted for numerical modelling, and the boundary substructure method is used for seismic wave input. On that basis, we conduct a comparative seismic analysis between 2D and 3D models. The results show that the ground motion distributions in the middle reef regions calculated by 2D and 3D models are generally consistent with each other. However, in the areas where the topography changes drastically, the 3D terrain shows an important influence on the local seismic response.

Earthquake ground motion modeling of induced seismicity in the Groningen gas field

AbstractA physics‐based numerical approach is used to characterize earthquake ground motion due to induced seismicity in the Groningen gas field and to improve empirical ground motion models for seismic hazard and risk assessment. To this end, a large‐scale (20 km × 20 km) heterogeneous 3D seismic wave propagation model for the Groningen area is constructed, based on the significant bulk of available geological, geophysical, geotechnical, and seismological data. Results of physics‐based numerical simulations are validated against the ground motion recordings of the January 8, 2018, ML 3.4 Zeerijp earthquake. Taking advantage of suitable models of slip time functions at the seismic source and of the detailed geophysical model, the numerical simulations are found to reproduce accurately the observed features of ground motions at epicentral distances less than 10 km, in a broad frequency range, up to about 8 Hz. A sensitivity analysis is also addressed to discuss the impact of 3D underground geological features, the stochastic variability of seismic velocities and the frequency dependence of the quality factor. Amongst others, results point out some key features related to 3D seismic wave propagation, such as the magnitude and distance dependence of site amplification functions, that may be relevant to the improvement of the empirical models for earthquake ground motion prediction.

3D Seismic Velocity Models for Alaska from Joint Tomographic Inversion of Body-Wave and Surface-Wave Data

AbstractWe present two new seismic velocity models for Alaska from joint inversions of body-wave and ambient-noise-derived surface-wave data, using two different methods. Our work takes advantage of data from many recent temporary seismic networks, including the Incorporated Research Institutions for Seismology Alaska Transportable Array, Southern Alaska Lithosphere and Mantle Observation Network, and onshore stations of the Alaska Amphibious Community Seismic Experiment. The first model primarily covers south-central Alaska and uses body-wave arrival times with Rayleigh-wave group-velocity maps accounting for their period-dependent lateral sensitivity. The second model results from direct inversion of body-wave arrival times and surface-wave phase travel times, and covers the entire state of Alaska. The two models provide 3D compressional- (VP) and shear-wave velocity (VS) information at depths ∼0–100 km. There are many similarities as well as differences between the two models. The first model provides a clear image of the high-velocity subducting plate and the low-velocity mantle wedge, in terms of the seismic velocities and the VP/VS ratio. The statewide model provides clearer images of many features such as sedimentary basins, a high-velocity anomaly in the mantle wedge under the Denali volcanic gap, low VP in the lower crust under Brooks Range, and low velocities at the eastern edge of Yakutat terrane under the Wrangell volcanic field. From simultaneously relocated earthquakes, we also find that the depth to the subducting Pacific plate beneath southern Alaska appears to be deeper than previous models.

Seismic evidence of glacial deposits inhibiting weathering of local bedrock at a snow-dominated subalpine watershed

Previously glaciated landscapes are often covered with glacial sediments with poorly sorted particles. The thickness of glacial sediments can reach hundreds of meters. These sediments, which have experienced high intensity erosion through glacial transportation, are susceptible to chemical weathering processes because of the increased reactive mineral surfaces induced via erosion. Infiltrated meteoric water will first attack the glacial sediments, becoming (partially) saturated with weathering products, before interacting with the local bedrock underneath. As a consequence, the glacial deposits will hinder the weathering processes of the underlying local bedrock. In this study, we test this hypothesis by imaging the weathered layer of a previously glaciated terrain in the Medicine Bow Mountains, Wyoming using full-3D seismic ambient-noise tomography. To the best of our knowledge, our study provides the first full-3D seismic velocity model of the Critical Zone structure under a previously glaciated landscape. Our 3D seismic velocity model reveals that the saprolite weathered from local bedrock is thinner where the overlying glacial deposit layer is thicker. This anti-correlation suggests that the glacial deposits may locally protect the underlying bedrock from chemical weathering by depleting reactive chemicals in the meteoric water and (partially) saturate the meteoric water with weathering products. Our study may provide a potential counter mechanism against glaciation-induced acceleration of chemical weathering of the continents, which regulates atmospheric concentration of carbon dioxide and the global climate.

Pseudo-3D seismic construction using tau-p transform interpolation

Three dimensional (3D) seismic imaging is very important in hydrocarbon exploration. However, 3D seismic data acquisition costs more expensive than 2D seismic data acquisition. Therefore, the explorations are mostly done with some 2D seismic lines and requiring some interpolation method to construct the 3D seismic model called Pseudo-3D Seismic. In other word, the 3D model depends much on the interpolation process for a more reliable result. There have been many interpolation methods used to construct the 3D seismic model. Tau-P Transform is one of the methods that can be used to construct a 3D seismic model. It has been used to reconstruct seismic data and fill the near-offset gap in marine seismic data for decades. In this research, the method is done by having the crossline of some 2D seismic lines and performing the transformation from t-x domain to the tau-p domain. After the transformation, by inverse-transformation from tau-p to t-x domain, we might perform interpolation along the line to construct more traces with regular and near spacing. This method can be performed to all crosslines and construct Pseudo-3D Seismic. The results show constructed crosslines with well-lineated layers. The crosslines show developed layers are like those of the inline implying that the interpolation successfully construct the layers based on the inline.