Earthquake Waveform Data Research Articles

Executing realistic earthquake simulations in unreal engine with material calibration

Earthquakes significantly impact societies and economies, underscoring the need for effective search and rescue strategies. As AI and robotics increasingly support these efforts, the demand for high-fidelity, real-time simulation environments for training has become pressing. Earthquake simulation can be considered as a complex system. Traditional simulation methods, which primarily focus on computing intricate factors for single buildings or simplified architectural agglomerations, often fall short in providing realistic visuals and real-time structural damage assessments for urban environments. To address this deficiency, we introduce a real-time, high visual fidelity earthquake simulation platform based on the Chaos Physics System in Unreal Engine, specifically designed to simulate the damage to urban buildings. Initially, we use a genetic algorithm to calibrate material simulation parameters from Ansys into the Unreal Engine’s fracture system, based on real-world test standards. This alignment ensures the similarity of results between the two systems while achieving real-time capabilities. Additionally, by integrating real earthquake waveform data, we improve the simulation’s authenticity, ensuring it accurately reflects historical events. All functionalities are integrated into a visual user interface, enabling zero-code operation, which facilitates testing and further development by cross-disciplinary users. We verify the platform’s effectiveness through three AI-based tasks: similarity detection, path planning, and image segmentation. This paper builds upon the preliminary earthquake simulation study we presented at IMET 2023, with significant enhancements, including improvements to the material calibration workflow and the method for binding building foundations.

Source characteristics of earthquakes in Delhi and its vicinity: Implications for seismogenesis in the stable continental region of India

Delhi and its surrounding region are among the important intraplate seismically active regions of India. According to the Bureau of Indian Standards, it lies in seismic zone IV and is capable of generating small to moderate earthquakes. This region has also experienced moderate to large earthquakes in the past due to its proximity to the Himalayan arc and its own tectonics. There is an urgent need to assess the source characteristics of earthquakes and their scaling relationships for a reliable and accurate estimation of seismic hazard. Source parameters and their scaling relations have been estimated for this region using well-located small to moderate earthquakes (Mw 2.3–5.1) that occurred during the period from 2000 to 2020. For this purpose, we investigated three components of earthquake waveform data using the ω−2 source model. The outcomes show the occurrence of low static stress drop (0.5–52.87 ​bars) in the Delhi region indicating approximately 57% of the events exhibit a stress drop < 10 ​bars, 27 % of events fall in the range of 10–20 ​bars, and only 16 % events exhibit stress drop > 20 ​bars. This observation suggests that the shallow subsurface of the study region may have low-strength material characteristics and a heterogeneous nature. In addition, the Zuniga parameter (ε) is estimated less than 1.0 by analyzing static and apparent stress drops, which infers the partial stress drop model fits very well in the study region. The seismic moment varies from 1.02×1012 to 1.03×1016 ​N.m. for P-wave and 6.46×1011 Nm to 7.54×1015 Nm for S-wave. The average seismic source radius lies in the range of 0.1–3.05 ​km with a ratio {r(p)/r(s)} of 1.5 ​km in the study region. The estimated values of corner frequency are comparatively lower for the S-wave (1.5–18.2 ​Hz) than for the P-wave (1.88–19.3 ​Hz) suggesting the ‘shifting properties’ of the corner frequency corroborated with the theoretical agreement. The seismic energy (E) is estimated using both P- and S-wave separately and its average value varies from 4.28×106 to 6.22×1011 ​J. The estimated stress drop and seismic moment demonstrate no correlation with each other. Therefore small to moderate-size earthquakes inherently follow the self-similarity behavior. The obtained scaling relationship between Seismic Moment and Corner Frequency is Mo=7.94∗1015fc−2.97. The derived scaling relations and source parameters are expected to provide a priori information for the assessment of seismic hazards and are useful in the simulation of strong ground motion characteristics in the region.

INSTANCE – the Italian seismic dataset for machine learning

Abstract. The Italian earthquake waveform data are collected here in a dataset suited for machine learning analysis (ML) applications. The dataset consists of nearly 1.2 million three-component (3C) waveform traces from about 50 000 earthquakes and more than 130 000 noise 3C waveform traces, for a total of about 43 000 h of data and an average of 21 3C traces provided per event. The earthquake list is based on the Italian Seismic Bulletin (http://terremoti.ingv.it/bsi, last access: 15 February 2020​​​​​​​) of the Istituto Nazionale di Geofisica e Vulcanologia between January 2005 and January 2020, and it includes events in the magnitude range between 0.0 and 6.5. The waveform data have been recorded primarily by the Italian National Seismic Network (network code IV) and include both weak- (HH, EH channels) and strong-motion (HN channels) recordings. All the waveform traces have a length of 120 s, are sampled at 100 Hz, and are provided both in counts and ground motion physical units after deconvolution of the instrument transfer functions. The waveform dataset is accompanied by metadata consisting of more than 100 parameters providing comprehensive information on the earthquake source, the recording stations, the trace features, and other derived quantities. This rich set of metadata allows the users to target the data selection for their own purposes. Much of these metadata can be used as labels in ML analysis or for other studies. The dataset, assembled in HDF5 format, is available at http://doi.org/10.13127/instance (Michelini et al., 2021).

Hypocenter and Magnitude Analysis of Aftershocks of the 2018 Lombok, Indonesia, Earthquakes Using Local Seismographic Networks

Abstract The island of Lombok in Indonesia is located between the Indo-Australian and Eurasian subduction trenches and the Flores back-arc thrust, making it vulnerable to earthquakes. On 29 July 2018, a significant earthquake Mw 6.4 shook this region and was followed by series of major earthquakes (Mw&amp;gt;5.8) on 5, 9, and 19 August, which led to severe damage in the northern Lombok area. In this study, we attempt to reveal the possible cause of the sequences of the 2018 Lombok earthquakes based on aftershock monitoring data. Twenty stations were deployed to record earthquake waveform data from 4 August to 9 September 2018. In total, 3259 events were identified using 28,728 P- and 20,713 S-wave arrival times during the monitoring. The aftershock hypocenters were determined using a nonlinear approach and relocated using double-difference method. The moment magnitude (Mw) of each event was determined by fitting the displacement spectrum amplitude using a Brune-type model. The magnitudes of the aftershocks range from Mw 1.7 to 6.7. The seismicity pattern reveals three clusters located in the Flores oceanic crust, which fit well with the occurrences of the four events with Mw&amp;gt;6. We interpret these events as the main rupture area of the 2018 Lombok earthquake sequence. Furthermore, an aseismic zone in the vicinity of Rinjani extending toward the northwestern part of Lombok was observed. We propose that the crust in this area has elevated temperatures and is highly fractured thus inhibiting the generation of large earthquakes. The aseismic nature is therefore an artifact of the detection threshold of our network (Mw 4.6).

Hypocenter Determination Using a Non-Linear Method for Events in West Java, Indonesia: A Preliminary Result

West Java, part of the Sunda Arc, has relatively high seismicity due to subduction activity and faulting. The first step of tomography study in order to infer the geometry of the structure beneath West Java is to conduct precise earthquake hypocenter determination. In this study, we used earthquake waveform data taken from the regional Meteorological, Climatological, Geophysical Agency (BMKG) network from South Sumatra to central Java. We have repicked P and S arrival times from about 800 events in the period from April 2009 to December 2015. We selected the events which have azimuthal gap < 210° and phase more than 8. The non-linear method employed in this study used the oct-tree sampling algorithm from NonLinLoc program to determine the earthquake hypocenters. The hypocenter location results give better clustering earthquakes which are correlated well with geological structure in the study region. We also compared our results with BMKG catalog data and found that the average hypocenter location difference is about 12 km in latitude direction, 9.5 km in longitude direction, and the average focal depth difference is about 19.5 km. For future studies, we will conduct tomographic imaging to invert 3-D seismic velocity structure beneath the western part of Java.

Imaging Shallow Crustal Structure in the Upper Mississippi Embayment Using Local Earthquake Waveform Data

A 1D normal moveout (NMO)‐corrected and stacked pseudoprofiling method was applied to analyze the characteristic features shown on primary P ‐ and S ‐wave coda and on Sp waveforms from local microearthquakes in an attempt to image prominent reflectors and to resolve shallow crustal velocity structure (∼5 km) in the upper Mississippi embayment. Acoustic well log data were used to constrain the P ‐wave velocity in the upper 5 km. Events at close distances and with clear P and S arrivals were selected to ensure reliable NMO correction for reflections and transmissions. The observed reflections and transmissions are important controlling factors on modeling waveforms. We analyzed local earthquake data recorded at all broadband and one short‐period station of the Cooperative New Madrid Seismic Network. Despite polarity differences among P , S , and Sp waveforms, consistent reflectors in the sedimentary section can be imaged across the three wave types. Correlation with a basement‐penetrating well indicates that reflectors at the base of the Upper Cretaceous–Holocene Mississippi Embayment Supergroup, the base of the Cambrian–Ordovician Knox Group, and the high‐velocity lower Upper Cambrian Bonneterre Formation are shown in pseudoprofiles among stations in the upper Mississippi embayment. Our study finds that a one‐layer homogeneous velocity model of sediments in the ranges of 1.95–2.42 km/s for V P and 0.60–0.73 km/s for V S overlying a half‐space of Paleozoic rocks with velocities in the ranges of 6.0–6.2 km/s for V P and 3.26–3.6 km/s for V S can represent shallow crustal structure in the upper Mississippi embayment. Differential times of P – PpPhp and S – SsShs appear linearly proportional to sediment thicknesses, which best fits a one‐layer sediment structure with average V P 2.042±0.041 km/s and V S 0.709±0.051 km/s, in the least‐squares sense predicted by the wave propagation effects. Online Material: Figures illustrating seismograms, process procedure, imaged reflectors, and resolved velocity structure for six broadband stations and one short‐period station.

Coda Q in Eastern Indian shield

We have analyzed 16 earthquake waveform data recorded during the period from 2006 to 2013 at broadband station lying at the premises of Indian School of Mines, Dhanbad in the Eastern Indian Shield region. Coda window lengths of 30, 40 and 50 s were selected after thorough analysis of the waveforms. The Coda Q (Qc) values were computed using single back scattered method. The earthquakes parameters were compiled from catalogue of Indian Meteorological Department (Nodal agency under Govt. of India for record keeping and data sharing), New Delhi. The estimated average Qc values for three coda windows 30, 40 and 50 s are Qc = 259.1f0.808, Qc = 275.9f0.764 and Qc = 397.1f0.651, respectively. The average Qc value estimated from the Qc values for the time windows 30, 40 and 50 s is found to be Qc = 313.2f0.73. Thus, the attenuation follows the power law relationships (e.g., Qc = Q0fn), and the moderate to higher values of frequency parameters (n) obviously show that the Qc value is a strong function of frequency. The increasing values of Q0 with increasing lapse time indicating the depth dependency of attenuation, and accounts for decreasing heterogeneity towards deeper level beneath the study area.

Preserved and modified mid-Archean crustal blocks in Dharwar craton: Seismological evidence

We report significant lateral variability in shear wave velocity and Moho depth in the Archean crust, beneath the Dharwar craton, using earthquake waveform data recorded over 50 broadband seismographs. The craton is a continuously exposed Archean continental fragment divided into the west Dharwar craton (WDC) of age 2.7–3.36Ga, and the east Dharwar craton (EDC) of age, dominantly, 2.5Ga. The craton progressively transitions into the Southern Granulite Terrain (SGT) with age of metamorphism around 2.6Ga.The inversion and modeling of receiver function data reveal significant variation of Moho depth, viz., 38–54km in the WDC, and 40–46km in the SGT and 32–38km in the EDC. The average shear wave velocity (Vs) of crust beneath the WDC is ∼3.85km/s as compared to ∼3.6km/s in the EDC. We infer highly variable thickness (16–30km) of mafic cumulate (Vs≥4.0km/s and Vp≥7.0km/s) beneath the WDC, in contrast with a thin one (<5km) beneath the late Archean EDC. The 3.36Ga greenstone belt in the WDC has maximum basal layer thickness of ∼30km. These results suggest the intermediate-mafic composition and exceptional thickness of crust beneath the WDC (>50km) as compared to felsic to intermediate composition for the EDC crust with almost flat Moho (down to ∼38km). These results suggest preserved mafic crustal root beneath the middle Archean terrain in the WDC that has remained inert since then. On the other hand, felsic to intermediate composition of crust with a nearly flat Moho beneath the late Archean EDC could be a consequence of regional delamination of lower crust. The preserved distinct Moho topography across the Archean terrains suggests it as compositional boundary. Considering the surface exposure of 15–20km crust, based on P–T condition, in the granulite segment of the WDC, we speculate a Himalaya-like crustal thickness (50–70km) beneath the middle Archean crust pointing toward a plate tectonic-like scenario at ∼3.0Ga.

Construction of normal fuzzy numbers: A case study with earthquake waveform data

This article demonstrates that a normal fuzzy number can be constructed from earthquake waveform data. According to the RandomnessFuzziness Consistency Principle, two independent laws of randomness in [α, β] and [β, γ] are necessary and sufficient to define a normal fuzzy number [α, β, γ]. In this article, we have shown how to construct normal fuzzy numbers using data from earthquake waveform and have studied the pattern of the membership curve

Upper mantle surprises derived from the recent Virginia earthquake waveform data

Recent high resolution regional waveform modeling reveals that the lithosphere beneath the North American craton is subdivided into an upper nearly uniform layer and a lower layer with a high velocity gradient. The boundary occurs at about a depth of 115km and is responsible for 8° discontinuity in seismic record sections that is often observed in craton environments. Unexpectedly, we find seismic velocities in the lower layer significantly reduced along a corridor from the New Madrid rift zone to Virginia. This reduced velocity in the lower lithosphere may be associated with a possible historic hotspot activity. We also find a well developed X-discontinuity that we model as a ∼3% increase in P velocity starting at a depth of ∼290km. These anomalous features transition into a nearly 1D craton structure to the north with a strong low-velocity anomaly just above the 410 discontinuity along an east–west boundary. The latter two features may be relics of structures formed from the descending Farallon plate between Late Cretaceous and Early Tertiary.

A crustal transect across the Oman Mountains on the eastern margin of Arabia

ABSTRACT The unique tectonic setting of the Oman Mountains and the Semail Ophiolite, together with ongoing hydrocarbon exploration, have focused geological research on the sedimentary and ophiolite stratigraphy of Oman. However, there have been few investigations of the crustal-scale structure of the eastern Arabian continental margin. In order to rectify this omission, we made a 255-km-long, southwesterly oriented crustal transect of the Oman Mountains from the Coastal Zone to the interior Foreland via the 3,000-m-high Jebel Akhdar. The model for the upper 8 km of the crust was constrained using 152 km of 2-D seismic reflection profiles, 15 exploratory wells, and 1:100,000- to 1:250,000-scale geological maps. Receiver-function analysis of teleseismic earthquake waveform data from three temporary digital seismic stations gave the first reliable estimates of depth-to-Moho. Bouguer gravity modeling provided further evidence of depths to the Moho and metamorphic basement. Four principal results were obtained from the transect. (1) An interpreted mountain root beneath Jebel Akhdar has a lateral extent of about 60 km along the transect. The depth-to-Moho of 41 to 44 km about 25 km southwest of Jebel Akhdar increased to 48 to 51 km on its northeastern side but decreased to 39 to 42 km beneath the coastal plain farther to the northeast. (2) The average depth to the metamorphic basement was inferred from Bouguer gravity modeling to be 9 km in the core of Jebel Akhdar and immediately to the southwest. A relatively shallow depth-to-basement of 7 to 8 km coincided with the Jebel Qusaybah anticline south of the Hamrat Ad Duru Range. (3) Based on surface, subsurface, and gravity modeling, the Nakhl Ophiolite block extends seaward for approximately 80 km from its most southerly outcrop. It has an average thickness of about 5 km, whereas ophiolite south of Jebel Akhdar is only 1 km thick. The underlying Hawasina Sediments are between 2 and 3 km thick in the Hamrat Ad Duru Zone, and 2 km thick in the Coastal Zone. (4) Southwest of Jebel Akhdar, reactivated NW-oriented strike-slip basement faults that deformed Miocene to Pliocene sediments were inferred from the interpretation of seismic reflection profiles.

A crustal transect across the Oman Mountains on the eastern margin of Arabia

The unique tectonic setting of the Oman Mountains and the Semail Ophiolite, together with ongoing hydrocarbon exploration, have focused geological research on the sedimentary and ophiolite stratigraphy of Oman. However, there have been few investigations of the crustal-scale structure of the eastern Arabian continental margin. In order to rectify this omission, we made a 255-km-long, southwesterly oriented crustal transect of the Oman Mountains from the Coastal Zone to the interior Foreland via the 3,000-m-high Jebel Akhdar. The model for the upper 8 km of the crust was constrained using 152 km of 2-D seismic reflection profiles, 15 exploratory wells, and 1:100,000to 1:250,000-scale geological maps. Receiver-function analysis of teleseismic earthquake waveform data from three temporary digital seismic stations gave the first reliable estimates of depth-to-Moho. Bouguer gravity modeling provided further evidence of depths to the Moho and metamorphic basement.

Crustal structure of the Indian Shield: New constraints from teleseismic receiver functions

Teleseismic earthquake waveform data from 10 broadband stations spread over the Indian shield and in operation since 1997, were analyzed to infer the crustal structure, using the receiver function technique. The South Indian shield is characterized by a 33–39 km thick, and remarkably simple crust, with an average Poisson's ratio close to 0.25. The Archaean crust is devoid of any prominent intra‐crustal discontinuities. The velocity contrast at the well developed Moho is large, resulting in very clear P‐to‐S conversions as well as first‐order multiples. In contrast, the predominantly Proterozoic crust in the northern part of the shield exhibits a complex character, due to the presence of additional seismic discontinuities. Moho conversions, which are considerably weaker compared to the Archaean terrains, indicate crustal thicknesses of more than 40 km.

Modeling of wave propagation in northern Los Angeles basin

AbstractThe Los Angeles basin is characterized by deep structural complexity and is the site of numerous earthquakes. We analyze the amplitude and waveform data of earthquakes recorded in the Los Angeles basin in order to identify the structurally controlled path effects. This has been done in order to determine which features of the structure affect the observations and to generate improved models in different parts of the basin increasing our capabilities of predicting seismic hazard. Several structural models of the L.A. basin that are based on regional subsurface studies, exposed sections, scattered oil wells, and other limited geophysical data have recently become available. In this study, we have used seismic modeling techniques together with geologic models to attempt to explain site variations in some important data bases. We have modeled waveforms of (1) the 19 January 1989 Malibu earthquake data recorded in Pasadena, (2) an M = 2.8 earthquake recorded by the USC downhole array in the Baldwin Hills, southern California, and (3) two aftershocks of the Whittier Narrows earthquake recorded at five stations along a profile.The modeling of the Malibu earthquake results in a layered one-dimensional model representing 6.5 km of layered sediment underlain by a high-velocity basement. Direct arrivals, basin reflected phases, and multiple reverberations are modeled fairly well by this one-dimensional model. The downhole array data in the Baldwin Hills show a significant near-surface amplification that can be modeled by very low-velocity near-surface materials. A series of aftershocks of the Whittier Narrows earthquake recorded at close distances at temporary recording sites shows a wide variation in peak accelerations due both to radiation pattern and propagation effects. The effect of lateral heterogeneity is evident in the travel time, where stations within the basin show later arrival times than those away from the basin for the same epicentral distance. Seismograms recorded at different sites show variation in waveforms due to multi-pathing of rays. We use such triplicated arrivals to constrain the structure of different interfaces. Using these criteria and the synthetic seismograms calculated by ray theory and finite difference methods, we have been able to model the tangential seismograms due to two of these events recorded at five stations along a two-dimensional profile.All three modeling exercises helped us understand wave propagation in the basin environment. A basin-reflected phase was identified in the seismogram from the Malibu earthquake, which was used to derive an effective depth of the basement. Near-surface amplification of the waves observed in the downhole data could be explained by constructive interference of the multiply reflected waves through the thin near-surface low-velocity layer. Similarly, site-dependent variation of waveform and travel time shown by the seismograms from the aftershocks of the Whittier Narrows, California, earthquake could be accounted for when a laterally varying structure was used.