Distribution Of Ground Motion Research Articles

Magnitude estimation and site characterization in southwestern British Columbia: application to earthquake early warning

In this study, we took a close look at the Ocean Networks Canada’s earthquake early warning system in southwestern British Columbia through analysis of the magnitude estimates by this system and characterization of site conditions for both onshore and offshore stations. Using magnitude values estimated at each station, over hundreds of notifications, we provided station terms to correct the magnitudes for stations that systematically generate high or low magnitude values. Moreover, by compiling a rich ground motion amplitude dataset and applying the horizontal-to-vertical spectral ratio method from Fourier amplitude of acceleration and response spectral acceleration, we investigated site characterization through evaluation of non-linear site response behavior and estimation of the site dominant frequency (fpeak) and its peak amplitude (Apeak) for each station. In general, no strong evidence of non-linearity is observed at any stations considering the magnitude-distance distribution of ground motions in this study. Offshore sites show fpeak and Apeak in the range of approximately 1.7–6 Hz and 0.4–1.2 (in base-10 log unit), respectively, whereas onshore sites show approximately 1–6 Hz for fpeak and 0.3–0.7 (in base-10 log unit) for Apeak.

Peak Acceleration Distribution on the Surface of Reef Islands under the Action of Vertical Ground Motion

This paper adopts the fluid–structure coupling algorithm based on the acoustic fluid element, the fluid dynamic artificial boundary, and the consistent viscoelastic artificial boundary of solid media to establish a finite element model of the dynamic interaction of the reef-island–seawater system. Then, a numerical simulation of the seismic response of the reef-island site is carried out to study the seismic ground motion distribution patterns of the reef–seawater site and the reef-island–lagoon site. The innovation of this article is that the influence of reef–island topography and fluid–structure coupling is considered in the analysis when vertical ground motion is input. The results show that the slope angle of the bottom layer has a significant influence on the peak ground acceleration distribution and peak size on the island slope surface and the reef platform. For high-frequency input motion, a smaller reef platform width will induce a larger peak acceleration response on the reef platform. Seawater has a significant suppressive effect on vertical ground acceleration. The more high-frequency components of the input bedrock motion, the more obvious this suppression effect will be. The existence of the lagoon will amplify the maximum peak acceleration on the reef platform. According to the calculation results, lagoon terrain can amplify the maximum horizontal and vertical peak accelerations on the reef platform by about 19 and 6 times relative to the free-field results, respectively.

A Physics-Based Seismic Risk Assessment of the Qujiang Fault: From Dynamic Rupture to Disaster Estimation

This study achieved the construction of earthquake disaster scenarios based on physics-based methods—from fault dynamic rupture to seismic wave propagation—and then population and economic loss estimations. The physics-based dynamic rupture and strong ground motion simulations can fully consider the three-dimensional complexity of physical parameters such as fault geometry, stress field, rock properties, and terrain. Quantitative analysis of multiple seismic disaster scenarios along the Qujiang Fault in western Yunnan Province in southwestern China based on different nucleation locations was achieved. The results indicate that the northwestern segment of the Qujiang Fault is expected to experience significantly higher levels of damage compared to the southeastern segment. Additionally, there are significant variations in human losses, even though the economic losses are similar across different scenarios. Dali Bai Autonomous Prefecture, Chuxiong Yi Autonomous Prefecture, Yuxi City, Honghe Hani and Yi Autonomous Prefecture, and Wenshan Zhuang and Miao Autonomous Prefecture were identified as at medium to high seismic risks, with Yuxi and Honghe being particularly vulnerable. Implementing targeted earthquake prevention measures in Yuxi and Honghe will significantly mitigate the potential risks posed by the Qujiang Fault. Notably, although the fault is within Yuxi, Honghe is likely to suffer the most severe damage. These findings emphasize the importance of considering rupture directivity and its influence on ground motion distribution when assessing seismic risk.

The 3D Physics-Based Broadband Ground-Motion Simulation, including Topography Effects Causing Damage to Structures, for the 2022 Mw 6.6 Menyuan, China, Earthquake

ABSTRACT On 8 January 2022, Menyuan County, China, was struck by an Mw 6.6 earthquake that caused surface rupture in the epicentral area and severe damage to an important railway bridge. The earthquake was recorded by only one strong-motion station, which presents a challenge for quantitatively estimating the extent of the ground-motion distribution caused by this event. In this study, the spectral element method (SPECFEM3D code), which solves the elastodynamic equations and can capture the full physics of seismic-wave propagation, is employed for broadband (0–10 Hz) ground-motion simulations of this earthquake. A hybrid kinematic source is developed in which the final slip distribution combines a prescribed asperity model based on Interferometric Synthetic Aperture Radar data (as a source for low-frequency radiation) and a stochastic part (as a source for high-frequency radiation), which introduces spatial heterogeneities to the prescribed asperity model. The numerical approach is first validated by modeling the well-recorded 1994 Northridge earthquake before modeling the Menyuan earthquake. The simulated ground motion is compared with the only observed strong-motion station record, as well as with empirical Next Generation Attenuation-West2 ground-motion models. Then, topography effect in Menyuan earthquake is studied in detail. The simulated ground motions with and without surface topography indicate that the topography tends to focus and scatter the seismic wavefield, resulting in amplification of the ground shaking. The results show a significant correlation between the peak ground velocity (PGV) and topography. The PGV amplification caused by topography effects is period dependent, and its peak amplification reaches up to 50% within a typical resonance period (1–2 s). It could be inferred that the railway bridge probably vibrated in resonance and suffered severe damage owing to the amplified long-period ground motion caused by the topography.

Analysis of Strong Ground Motion Characteristics for the Jishishan MS6.2 Earthquake December 18, 2023

The MS6.2 earthquake occurred in Jishishan, Gansu Province, China, on December 18, 2023. Based on some strong seismic acceleration time histories captured by some stations of China National Strong Earthquake Observation Network and National Earthquake Early Warning Network, the spatial distribution characteristics, rupture directivity effect, hanging wall and footwall effect, response spectrum characteristics, and attenuation of the peak ground acceleration (PGA) were analyzed in this paper. It can be used as reference for the site determination of post‐earthquake reconstruction and seismic design of engineering structures. The analysis shows that the spatial distribution of strong ground motion of the Jishishan MS6.2 earthquake is mainly controlled by the distribution of causative fault. Near the fault, the effect of rupture directivity is obvious. The effect of hanging wall and footwall significantly affects the distribution of PGAs for this earthquake, causing a pronounced asymmetric pattern about PGAs relative to the fault, with slower attenuation on the hanging wall compared to the footwall. The type of site obviously affects the characteristics of response spectrum. The ground motion intensity observed at the epicenter of this earthquake significantly exceeded the levels of rare and extremely rare seismic events in the current seismic design codes. The attenuation relationship of PGA obtained by regression analysis shows that ones in the 5th generation Chinese ground motion parameter zoning map for the Qinghai‐Tibet region underestimate the horizontal PGA.

Spatial distribution of ground motion during the 2018 Northern Osaka earthquake (Mw5.6) based on a microtremor survey in Ibaraki city

Spatial distribution of ground motion during the 2018 Northern Osaka earthquake (Mw5.6) based on a microtremor survey in Ibaraki city

Deterministic seismic hazard analysis from physics-based earthquake simulations in the Eastern Betics (SE Iberia)

The low frequency of large destructive earthquakes in the Eastern Betics (SE Iberian Peninsula), not recorded in the instrumental seismic catalog, complicate the estimation of the maximum ground motion that could be reached. Knowing the characteristics and behavior of these large seismic ruptures is crucial for the study of seismic hazard. In this work, we have used a physics-based earthquake simulator to generate a 100 kyr catalog of seismic ruptures associated with seismogenic faults bordering the quaternary Guadalentin and Bajo Segura basins. From these ruptures, we have selected maximum earthquake scenarios, and those associated with certain probabilities of exceeding a severe magnitude from the synthetic catalog. The estimation of maximum peak accelerations (PGA) by means of ground motion prediction equations include a possible site amplification that we have calculated from a detailed geotechnical classification of soils. According to the simulations, the modeled faults have the capacity to generate maximum earthquakes with magnitudes ranging MW 6.7–7.4. Densely populated urban areas located along the Guadalentin valley, such as Lorca, could be subject to site-dependent PGA values close to 0.6 g on the Alhama de Murcia fault trace. Similar ground motion would affect the coastline of SE Alicante province when evaluating the maximum simulated event in the Bajo Segura offshore fault. But already from magnitudes around MW ∼ 6, PGA estimations exceed critical values of 0.5 g at the south side of the Bajo Segura basin and the city of Murcia, highly dependent of ground-motion amplification induced by thick deposits of very soft and saturated soils. Our scenarios reflect that other factors such as fault geometry, kinematics and the capability observed in the simulations to generate multi-fault ruptures also affect the spatial distribution of maximum ground motion in this region. We expect that this evaluation could contribute as an improvement guideline for future strong motion prediction studies prior to the settlement of new urban infrastructures in the Eastern Betics.

A seismic risk assessment method for cultural artifacts based on the Law of Large Numbers

Earthquakes can cause significant damage to cultural artifacts, which often hold significant historical or cultural value. Seismic risk assessments can contribute to a more targeted approach by museum staff to the preventive conservation of cultural artifacts. The primary objective of this research is to suggest a new approach for assessing the seismic risk of cultural artifacts. This innovative method is founded on the Law of Large Numbers and aims to provide a more user-friendly way of evaluating the likelihood of potential seismic threat to cultural artifacts. The proposed method takes into account the statistical distribution of seismic ground motion and the seismic response characteristics of artifacts, and its accuracy and practicality are demonstrated by case studies. Compared with existing methods, the proposed method has the advantages of theoretical simplicity, low computational effort, and easier to be understood and mastered by museum staff. Furthermore, the impact of sample size on the assessment results was investigated. The findings demonstrate that the proposed method represents a valuable tool for cultural heritage risk decision-makers to evaluate the seismic risk of artifacts. By using this method, they can more effectively assess the potential damage caused by seismic effects and design suitable mitigation measures accordingly.

Analysis of Peak Ground Acceleration and Seismogenic Fault Characteristics of the Mw7.8 Earthquake in Turkey

A Mw7.8 earthquake struck Turkey on 6 February 2023, causing severe casualties and economic losses. This paper investigates the characteristics of strong ground motion and seismogenic fault of the earthquake. We collected and processed the strong ground motion records of 379 stations using Matlab, SeismoSignal, and Surfer software: Matlab (Version R2016a), SeismoSignal (Version 5.1.0), and Surfer (Version 23.0.15), and obtained the peak ground acceleration (PGA) contour map. We analyzed the near-fault effect, the fault locking segment effect, and the trampoline effect of the earthquake based on the spatial distribution of PGA, the fault geometry, and slip distribution. We found that the earthquake generated a very strong ground motion concentration effect in the near-fault area, with the maximum PGA exceeding 2000 cm/s2. However, the presence of fault locking segments influenced the spatial distribution of ground motion, resulting in four significant PGA high-value concentration areas at a local dislocation, a turning point, and the end of the East Anatolian Fault. We also revealed for the first time the typical manifestation of the trampoline effect in this earthquake, which was characterized by a large vertical acceleration with a positive direction significantly larger than the negative direction. This paper provides an important reference for understanding the seismogenic mechanism, damage mode, characteristics, and strong earthquake law of the Turkey earthquake.

Estimation of the Restoration Period of the Water Supply System in Lima, Peru, After a Scenario Earthquake

The restoration period of the water supply system in Lima, Peru, after a scenario earthquake was estimated in this study. To achieve the objective, the probabilistic assessment model for post-earthquake residual capacity of the utility lifeline system initially proposed by Nojima and Sugito (2005) and revised by following related studies was employed. The dataset of water distribution pipelines was provided by Potable Water and Sewer System Service in Lima, Peru (SEDAPAL), and the spatial distribution of ground motion with a moment magnitude of 8.6 was considered as a scenario earthquake in this study. The water disruption was anticipated to continue for approximately one month in certain districts of Lima, Peru. The estimated smallest water supplying ratio was 21.1% in Villa El Salvador after the scenario earthquake.

Seismic Response Analysis of a Shield Tunnel in a Coastal Nuclear Power Plant under a Complex Foundation

As a transportation hub connecting sea and land, the seismic safety of an undersea tunnel is very important. Based on the structural and stress characteristics of a shield tunnel, a seismic response analysis of a coastal nuclear power plant under a complex foundation is carried out in this paper. Firstly, adopting the lateral and longitudinal response displacement methods, the authors study the variation and distribution features of the rate of diameter change and joint-stretching value of the shield tunnel segments. On this basis, a three-dimensional refined finite element model of a sinking tube–soil mass under a complex soil foundation is established. Finally, when the joints and segments of the shield tunnel are subjected to ground motion, the deformation and internal force distribution of its lining segments are studied. The findings show that under influence of SL-2-magnitude ground motion, the soft–hard stratum junction is the weak point of the shield tunnel structure’s longitudinal seismic resistance. When the silt layer at the position of the shield segment is thicker and the geological conditions are relatively poorer, the internal force, diameter deformation rate, and joint-stretching value will be larger. The research results can provide a reference for seismic research on shield tunnels in sea areas under complex foundations.

Accelerating low-frequency ground motion simulation for finite fault sources using neural networks

SUMMARYIn the context of early emergency response to moderate and large earthquake shaking, we present a simulation based low-frequency ground motion estimation workflow that expedites an existing simulation method while taking into account simplified source process information. We focus on using source information that can be expected to be available shortly after an impacting earthquake, for example moment-tensor and simple finite-fault parameters. We utilize physics-based simulations which can include effects based on source orientation or finite faults, like rupture directivity. In order to keep the computational effort within feasible bounds and to apply the approach on global scale, we restrict ourselves to a low-frequency setup (standard 1-D layered earth model and 2 Hz sampling frequency) for either a moment tensor or a simple kinematic finite fault model. From the simulated records we then extract ground motion parameters of interest for arbitrary locations within the area of expected impact and display the expected spatial patterns of ground motion. Although simulations are kept simple, the results from this low-frequency ground motion parameter simulation (e.g. for peak-ground displacement) are in good agreement with observations from two well-studied earthquakes and partially more accurate than traditional, more empirical approaches (standard deviation <0.3 log10 units). However, waveform calculation and subsequent ground motion parameter extraction is computationally expensive. For a significant computational speedup in the context of rapid ground motion assessment, we directly train neural network (NN) models from large sets of source model information and their corresponding spatial ground motion distribution. We show that the trained NNs are able to reproduce the earthquake source related effects, like directivity and focal mechanism patterns, of the ground motion in any case. Given a set of source parameters, we obtain prediction errors smaller than 0.05 log10 units (ca. 11 per cent) and a magnitude dependent increase in computational speed of more than 1000 times compared to the initial waveform modelling. The proposed procedure enables thus to immediately compute probabilistic ground motion maps related to uncertainties in source parameters estimates, for example by sampling distributions based on parameter uncertainties or directly from an existing ensemble of focal parameter solutions.

Seismoacoustic Coupled Signals from the 11 July 2020 Ms 5.1 Tangshan, China, Earthquake

ABSTRACT The Ms 5.1 Tangshan earthquake that occurred on 11 July 2020 was recorded by the infrasound array DQS at a source-to-receiver distance of 196 km and an azimuth of 278°. Relatively high-apparent velocity, celerity of epicenter infrasound, and propagation modeling indicate a stratospheric arrival. The backprojection of the epicentral infrasound detection delineates a northeast direction-extended infrasound radiation region with a long axis of about 57 km and a short axis of about 28 km, which is in good agreement with the fault rupture direction. The robustness of the infrasound radiation source location is also tested. The consistency between the spatial distribution of the radiation source and the epicenter confirms that the extended radiating zone around the epicenter excited infrasound signals lasting 2.5 min at a distance of 196 km. A comparison between the backprojected sound pressure level and peak surface pressure derived from measured seismic ground motions shows some disagreement, which may involve propagation path and/or topography around the epicenter. Therefore, these factors should be taken into account when locating the sources of infrasound and estimating the distribution of ground motion. This study shows the ability of infrasound arrays to detect, locate, and research moderate earthquakes and help reconstruct the seismoacoustic coupling in the source region and fault rupture. Moreover, the complexity of the infrasound radiation source and seismoacoustic coupling mechanism is recognized. It is expected that infrasonic observations of moderate earthquakes will increase with the number of infrasound arrays deployed worldwide. Our study is also helpful to the scientific design and optimal layout of infrasound monitoring systems, which will allow for the detection of earthquakes in addition to explosive sources.

Quantification of rupture directivity effects on strong ground motion during the 8 January 2022 MS6.9 Menyuan earthquake in Qinghai, China

On 8 January 2022, an MS6.9 earthquake occurred in the Menyuan county, Qinghai province at the northeastern margin of the Tibetan Plateau. A dense observatory network consisting of accelerographs and intensity meters has obtained many acceleration recordings in this region, which previously had only a few strong motion recordings. Using acceleration data recorded by 141 accelerographs and micro-electro mechanical system (MEMS)-based intensity meters within 100 km of the causative fault, we investigated the spatial distribution and attenuation characteristics of the near-source ground motion during this event. The observed response spectra were compared with the prediction obtained using the NGA-West2 models. It was found that, in the long-period section of >1.0 s, the acceleration response spectra in the rupture forward direction (southeast of the epicenter) were greater than the prediction, while observations on the northwest side were lower than the prediction. Through the spatial distribution of the ground motion and quantitative analysis of the residuals, we found that the rupture directivity effects on the ground motions were controlled by the spatial azimuth relative to the fault and the along-strike projected length of the rupture, which mainly affected the long-period portion of the >1.0 s. In the rupture forward direction, the spectral accelerations (SAs) with periods of 1.0–10.0 s were enhanced to 1.18–1.56 times the average. In the backward direction (northwest of the epicenter), the SAs with periods of 1.0–10.0 s were only 0.63–0.86 times the average. The rupture directivity effects during the MS6.9 (MW6.6) earthquake exhibited an obvious period-dependence and narrowband characteristics, and the amplification effects were the strongest at 5.0 s. The amplification factors in the straight forward directions were underestimated by the empirical model. Two typical velocity pulse records were observed in the rupture forward direction, and their response spectra were significantly amplified at long periods of greater than 1.0 s, with peak amplification values of 4.0–6.0 near the characteristic period of the pulses. This amplification was related to the resonance excited by a specific periodic pulse. Our study provides a reference of quantifying near-source effects for both moderate and major shallow crustal earthquakes by using MEMS recordings in this region.

Distinctive seismic reflections from the subducting Pacific slab for earthquakes in the Ryukyu arc

SUMMARY During moderate to deep (35–260 km) earthquakes within the Philippine-sea slab along the Ryukyu arc, distinctive later phases after S are observed across the Japanese archipelago for epicentral distances from 1500 to 2200 km, producing anomalous amplification of ground motion in central and northern Japan. Broad-band observations show that these later phases have a faster apparent wave speed (7–9.5 km s−1) than S, and are dominant at low frequencies (0.05–1 Hz), indicating S-wave reflections returned from the upper mantle with strong attenuation for high frequencies. Numerical simulation of seismic wave propagation in 3-D models including subduction of both the Pacific (PAC) and Philippine-sea (PHS) plates reveal the origin of these reflections. The triplicated S wave front from the 410 km discontinuity undergoes wide-angle reflection at the top of the Pacific slab bringing strong amplitudes in a narrow band of epicentral distance near 1500 km. Also, wide-angle S reflections at the 660 km discontinuity are reinforced by refraction when travelling through the high-wave speed Pacific slab; these arrive at the surface beyond 2000 km epicentral distance. The characteristics of the deep mantle reflections and the distribution of large ground motion across Japan due to the reflections are strongly dependent on the source depth and distance to the Ryukyu earthquakes. Tomographic imagery for western Japan indicates loss of the high-wave speed signal of the PAC slab below 200 km depth; the character of the large S reflections and pattern of enhanced ground motions favours a model in which the PAC slab is thinned rather than fully broken. The peculiar pattern of ground motion from Ryukyu earthquakes can be useful for constraining deep slab structures that are difficult to identify based on tomography.

Dynamic simulations of coseismic slickenlines on non-planar and rough faults

SUMMARY Knowing the directions of rupture propagation of palaeo-earthquakes is a challenging, yet important task for our understanding of earthquake physics and seismic hazard, as the rupture direction significantly influences the distribution of strong ground motion. Recent studies proposed a relationship between the direction of rupture propagation and curvature of slickenlines formed during seismic slip. The relationship was established using a global catalogue of historic surface-rupturing earthquakes and dynamic models of idealized, planar faults. At the same time, some slickenlines previously documented on geometrically complex fault segments show their convexity opposite from the simple model prediction, which we refer to as ‘abnormal convexity’. To explain such observations, we perform simulations of spontaneous earthquake ruptures on non-planar and rough faults. We find that in the case of strike-slip faults, a non-planar fault model can lead to abnormal convexity of slickenlines in places where the fault dip angle changes abruptly from the average dip of the fault. Abnormal convexity of slickenlines is produced when the initial along-dip stresses are larger than, and are opposite in direction to, the dynamic stresses imparted by the mixed-mode rupture. Such results are also confirmed in our rupture simulations with a rough fault. Our results also show that the parameter space for which abnormal convexity of slickenlines occurs near Earth’s surface is narrow, especially when the fault strength and initial shear stresses increase with depth. Nevertheless, slickenlines on geometrically complex faults need to be carefully interpreted and investigation of rupture direction using curved slickenlines should focus on structurally simple parts of faults.

Large‐scale ground motion simulation of the 2016 Kumamoto earthquake incorporating soil nonlinearity and topographic effects

AbstractA large‐scale physics‐based simulation is conducted to investigate ground motion distribution in the Mw 7.0 2016 Kumamoto earthquake, Japan. The model simulates the earthquake scenario from fault rupture to wave propagation, and localized site response with consideration of the combined effect of soil nonlinearity and topographic amplification. The simulation domain is 51 km × 43 km × 25 km, and the obtained ground motion time histories are compared satisfactorily with recordings from KiK‐net and K‐NET. Ground motion distribution considering nonlinear soil response and topographic amplification is presented. A 3D equivalent linear model is developed to mimic the soil nonlinearity, and it is demonstrated that neglecting soil nonlinearity could over‐predict peak ground acceleration (PGA) and underestimate peak ground velocity (PGV) near the fault. The topographic amplification factors (TAFs) of PGA and PGV are found between 0.5 and 2.0, with a correlation coefficient of 0.7 between them. Predictive equations are proposed to correlate TAFs of PGA and PGV with topographic features, which are represented by relative heights obtained at different length scales. Finally, major earthquake damages are summarized with reference to the obtained ground motion intensity map.

An Earthquake Early Warning Method Based on Bayesian Inference

Earthquake early warning (EEW) systems can give people warnings before damaging ground motions reach their site and can reduce earthquake-related losses. It has been shown that Bayesian reference can be used to estimate earthquake magnitude, location, and the distribution of peak ground motion using observed ground-motion amplitudes, predefined prior information, and appropriate attenuation relationships. In this article, we describe a Bayesian approach to earthquake early warning (EEW) systems for the estimation of magnitude (M) and peak ground-motion velocity (PGV) using the Gutenberg–Richter relation as a priori probability derived from statistical historical earthquake information from the Japanese KiK-net. Moreover, using the magnitude Mj = 4.5 and PGV = 0.4 cm/s as the warning threshold, an earthquake hazard discrimination model was established. Following this, the proposed approach was compared with the traditional fitting method to analyze the earthquake hazard discrimination using an Mj = 4.3 earthquake in the Mt. Fuji area and an Mj = 5.5 earthquake in the Ibaraki area of Japan as examples. The results are as follows: (1) The probabilistic algorithm founded on the predictive model of the magnitude from the average period (τc) and PGV from the displacement amplitude (Pd) from the initial 3 s of the P wave is able to provide a fast and accurate estimation of the final magnitude and location. (2) The Bayesian inference approach for the earthquake hazard discrimination model has a 2.94% miss rate and a 5.88% false alarm rate, which is lower than that of the traditional fitting method, thus increasing the accuracy and reliability of earthquake hazard estimation.

Seismic wavefield reconstruction based on compressed sensing using data-driven reduced-order model

SUMMARYReconstruction of the distribution of ground motion due to an earthquake is one of the key technologies for the prediction of seismic damage to infrastructure. Particularly, the immediate reconstruction of the spatially continuous wavefield is valuable for decision-making of disaster response decisions in the initial phase. For a fast and accurate reconstruction, utilization of prior information is essential. In fluid mechanics, full-state recovery, which recovers the full state from sparse observation using a data-driven model reduced-order model, is actively used. In this study, the framework developed in the field of fluid mechanics is applied to seismic wavefield reconstruction. A seismic wavefield reconstruction framework based on compressed sensing using the data-driven reduced-order model (ROM) is proposed and its characteristics are investigated through numerical experiments. The data-driven ROM is generated from the data set of the wavefield using the singular value decomposition. The spatially continuous seismic wavefield is reconstructed from the sparse and discrete observation and the data-driven ROM. The observation sites used for reconstruction are effectively selected by the sensor optimization method for linear inverse problems based on a greedy algorithm. The proposed framework was applied to simulation data of theoretical waveform with the subsurface structure of the horizontally stratified three layers. The validity of the proposed method was confirmed by the reconstruction based on the noise-free observation. Since the ROM of the wavefield is used as prior information, the reconstruction error is reduced to an approximately lower error bound of the present framework, even though the number of sensors used for reconstruction is limited and randomly selected. In addition, the reconstruction error obtained by the proposed framework is much smaller than that obtained by the Gaussian process regression. For the numerical experiment with noise-contaminated observation, the reconstructed wavefield is degraded due to the observation noise, but the reconstruction error obtained by the present framework with all available observation sites is close to a lower error bound, even though the reconstructed wavefield using the Gaussian process regression is fully collapsed. Although the reconstruction error is larger than that obtained using all observation sites, the number of observation sites used for reconstruction can be reduced while minimizing the deterioration and scatter of the reconstructed data by combining it with the sensor optimization method. Hence, a better and more stable reconstruction of the wavefield than randomly selected observation sites can be realized, even if the reconstruction is carried out with a smaller number of observations with observation noise, by combining it with the sensor optimization method.

Estimation of ground motion due to induced seismicity at a geothermal power plant near Munich, Germany, using numerical simulations

In the North Alpine Foreland Basin, especially in the greater Munich area, several geothermal plants exploit a deep hydrothermal reservoir. So far at three sites events with ML>2.0 were detected, in an otherwise seismically inactive region. In this study we investigate a site east of Munich, where moderate seismicity started to appear around five years after the beginning of geothermal circulation. Two larger events (ML2.1/1.8) occurred in December 2016, followed by an additional ML2.1 event about 10 months later in September 2017. All three events occurred at about 3 km depth and were felt by the population. As this is a densely inhabited area, the estimation of the maximum ground motion and its distribution are of great importance for the authorities and the public. We perform 3D seismic simulations of the main events using the spectral element code SALVUS. The results can supplement recorded and macroseismic data in order to estimate the possible seismic impact in the area. In addition, we evaluate the influence of the uncertainties contained in the event parameters and in the subsurface model on the maximum peak ground velocity (PGV) values to calibrate the simulations. The simulated waveforms are mostly in good agreement with the ground motion recordings. Furthermore, the ground motion distribution coincides with the macroseismic data. According to the simulation results, even the largest event in the area did not exceed the critical PGV value of 5 mm/s defined by German norms and therefore had no damage potential. Such a numerical approach can help to improve the seismic monitoring network, identify affected zones and mitigate the seismic risk.