Large Earthquakes Research Articles

Impact of Multiple Faults on the Maximum Credible Ground-Motion Parameters of Large Earthquakes at a Near-Field Site

The ground-motion simulation of regional-specific earthquake scenarios is crucial for the seismic design of key facilities. Herein, we considered parameter uncertainty in ground-motion simulations and the impact of multiple faults when determining the maximum credible ground-motion parameters of large earthquakes at a near-field dam. The source models of the Daju–Lijiang, Xiaozhongdian–Daju, and Longpan–Qiaohou faults were established based on geological and geophysical data. Although the method for identifying asperity is not yet mature and still faces many difficulties, it provides an opportunity to identify the non-uniform slip distribution on the rupture plane by earthquake scenarios. A multi-scheme stochastic finite-fault simulation method was then used to estimate the minimum; mean; maximum; and 50th-, 84th-, and 95th-percentile values of the peak ground acceleration and pseudo-spectral acceleration response spectra. The results showed that the Longpan–Qiaohou fault can generate the largest ground-motion parameters compared with the other two faults. Moreover, this result was supported by the statistical analysis of the results of twelve thousand simulations of these three faults. Thus, it can be concluded that the maximum credible ground-motion parameters are represented by the 84th-percentile pseudo-spectral acceleration response spectrum of the Longpan–Qiaohou fault. This finding will benefit the seismic safety design of the target dam. More importantly, this multi-scheme method can be applied to other key facilities to obtain reasonable ground-motion parameters.

Detectability of low-viscosity zone along lithosphere–asthenosphere boundary beneath the Nankai Trough, Japan, based on high-fidelity viscoelastic simulation

After the 2011 Tohoku-oki earthquake, a seafloor observation system observed rapid landward deformation. These seafloor observation data are potentially explicable via modeling of a low-viscosity zone under the subducting plate, called the lithosphere–asthenosphere boundary (LAB). However, the effect of a low-viscosity LAB has not been empirically examined in past earthquakes because of the absence of seafloor observation data, which are expected to have high sensitivity in the detection of a low-viscosity LAB. The Nankai Trough, southwest Japan, is one location where seafloor geodetic stations are in operation that could detect a low-viscosity LAB after a future earthquake. Therefore, we quantitatively model how the low-viscosity of the LAB is expected to affect postseismic crustal deformation following an anticipated future large earthquake under the Nankai Trough. Calculating viscoelastic deformation using a model that takes into account the realistic crustal structure in the southwestern Japanese Archipelago, we examine the effects of LAB viscosity on surface deformation patterns. The results show for very low LAB viscosities (2.5×1017\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2.5 \ imes 10^{17}$$\\end{document} Pa s), rapid landward displacement as large as 38 cm/yr occurs in the offshore area, with uplift and subsidence patterns highly dependent on the viscosity structure. Especially in the first year after the earthquake, the difference in deformation between the cases with and without a low-viscosity LAB was much larger than the observational error level of the current seafloor observation system. For such low LAB viscosities, the probability of detection is therefore high. On the other hand, for moderately low LAB viscosities (2.5×1018\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2.5 \ imes 10^{18}$$\\end{document} Pa s), the deformation patterns in the cases with and without a low-viscosity LAB are similar. Indeed, the difference in displacement lies within the observational error level of the current observational network, so detection is expected to be difficult for a LAB of only moderately low-viscosity. However, such a LAB may be detected by improving observational accuracy in the Global Navigation Satellite System–acoustic observation technique by performing more frequent measurements. Additional detection potential lies in expected future accuracy improvements in vertical displacement estimates at the DONET stations.Graphical

Ring-shaped seismicity structures in the region of Kamchatka: possible preparation for great earthquake

We have been studying some seismicity characteristics in the region of Kamchatka region. It was established that two pairs of ring-shaped seismicity structures at depths of 0-33 and 34-70 km have been formed here in 1973-2018 prior to large earthquakes (05.12.1997 г., Mw=7.8 and 20.12.2018, Mw=7.3). Ring-shaped structures are characterized by threshold magnitude values (Mt1 and Mt2 correspondingly) and also big axes length (L1 and L2). Ring-shaped structures were identified in the area to the east and northeast of Petropavlovsk-Kamchatskiy city, where no great earthquakes have occurred during more than 60 years (ring-shaped structure was identified also in the depth range of 71-110 km here). Earlier, correlation dependences of Mt1 and Mt2 parameters on Mw values of major earthquakes for the west of Pacific were creating. Using these dependencies, the magnitude of possible great earthquake in this area was estimated as Mw=8.6±0.2. Besides that, a conclusion on the source depth of such event was drawing on the base of the analysis of three ring-shaped structures. The reasons for ring-shaped structures formation in different depth ranges of the subduction zones are discussing.

A strainmeter array as the fulcrum of novel observatory sites along the Alto Tiberina Near Fault Observatory

Abstract. Fault slip is a complex natural phenomenon involving multiple spatiotemporal scales from seconds to days to weeks. To understand the physical and chemical processes responsible for the full fault slip spectrum, a multidisciplinary approach is highly recommended. The Near Fault Observatories (NFOs) aim at providing high-precision and spatiotemporally dense multidisciplinary near-fault data, enabling the generation of new original observations and innovative scientific products. The Alto Tiberina Near Fault Observatory is a permanent monitoring infrastructure established around the Alto Tiberina fault (ATF), a 60 km long low-angle normal fault (mean dip 20°), located along a sector of the Northern Apennines (central Italy) undergoing an extension at a rate of about 3 mm yr−1. The presence of repeating earthquakes on the ATF and a steep gradient in crustal velocities measured across the ATF by GNSS stations suggest large and deep (5–12 km) portions of the ATF undergoing aseismic creep. Both laboratory and theoretical studies indicate that any given patch of a fault can creep, nucleate slow earthquakes, and host large earthquakes, as also documented in nature for certain ruptures (e.g., Iquique in 2014, Tōhoku in 2011, and Parkfield in 2004). Nonetheless, how a fault patch switches from one mode of slip to another, as well as the interaction between creep, slow slip, and regular earthquakes, is still poorly documented by near-field observation. With the strainmeter array along the Alto Tiberina fault system (STAR) project, we build a series of six geophysical observatory sites consisting of 80–160 m deep vertical boreholes instrumented with strainmeters and seismometers as well as meteorological and GNSS antennas and additional seismometers at the surface. By covering the portions of the ATF that exhibits repeated earthquakes at shallow depth (above 4 km) with these new observatory sites, we aim to collect unique open-access data to answer fundamental questions about the relationship between creep, slow slip, dynamic earthquake rupture, and tectonic faulting.

Effectiveness of countermeasure options for chemical facilities against the discharge of chemical substances into rivers caused by a large earthquake: case study of the Yodo river system in Osaka prefecture, Japan

Technological accidents triggered by natural hazards, which are commonly referred to as Natech events, are rare occurrences yet carry the potential for significant damage. Specifically, the release of hazardous chemicals into the aquatic environment and community water systems poses a grave threat to human health and society. Accordingly, we must conduct assessments that consider the potential consequences of these accidents. In this study, we examined the criteria for implementing spill protection measures to mitigate river spills of chemical substances using information on the amount of chemical substances and their toxicity. The countermeasure options readily available to employees at industrial plants and chemical storage sites where a chemical spill might originate included emergency shut-off valves, bunds and related spill containment structures, and other spill prevention measures. In this case study, a combination of countermeasure options was evaluated to examine the effectiveness of spill mitigation in the Yodo River located in the Kyoto Prefecture of Japan. Results of the case study showed that bunds were emerged as the most useful countermeasure option, reducing the probability of accidents occurring and impact of accidents. We also defined a methodology for calculating the chemical storage volumes appropriate for different countermeasures to ensure that the concentration of chemicals that could reach the water intake does not exceed the standard values. We believe that these methodologies can help chemical-handling companies make decisions when countermeasure options for responding to a chemical spill into a river. Chemical-handling companies can estimate the risk to downstream water treatment plants in the chemical spill, which can also help them consider mitigation measures.

Three-dimensional path-effect model to simulate ground motion attenuation on the Korean Peninsula

In low-to-moderately active seismic regions such as the Korean Peninsula, it is difficult to analyze seismic hazards because only a limited number of strong ground motions have been recorded. To address this shortcoming in the data, ground motion simulation can be used to generate the strong ground motions associated with potentially large earthquakes, taking into account the attenuation that occurs as the distance from the source increases. To simulate this attenuation, the path effect, which is a component of the Fourier amplitude spectrum ( FAS), needs to be defined, along with the source and site effects. The path effect represents the propagation of seismic rays through a tectonic medium. In this study, a three-dimensional (3D) path effect model is developed for the Korean Peninsula, consisting of a 3D geometrical spreading factor, quality factor, and shear-wave velocity. The accuracy of the proposed model is verified by comparing the path-effect values obtained from the FAS of individual ground motions recorded on the Korean Peninsula and those calculated from the model. Examples that demonstrate the procedure to calculate the 3D path effect for the Korean Peninsula are also provided.

Impact of the soil-foundation-structure interaction in the seismic behaviour of a heritage masonry tower: The Giralda of Seville

The seismic safety of heritage buildings may be affected by the interaction between the soil, the foundation and the structure, which is usually neglected in conventional seismic assessments. These factors are particularly important in the case of slender constructions, such as masonry towers, over soft strata. Hence, this work deals with the influence of the soil-foundation-structure interaction in the seismic behaviour of complex heritage masonry towers. The investigations have been carried out considering the case study of the Giralda tower in Seville, Spain. The region is an earthquake-prone area, characterised by far away very large earthquakes with long-return periods. The Giralda tower is a slender brick unreinforced masonry tower, 95 m high and about 13 m wide. It features a high artistic value and popularity as it has been the historical symbol of the city. It was declared a UNESCO Word Heritage Site of Outstanding Universal Value in 1987. Apart from its slenderness, the tower presents some other seismic vulnerabilities: openings irregularities, material heterogeneity and the position of a belfry on the top. Furthermore, the building is placed on soft alluvial strata and has a shallow foundation. Likewise, the tower has a considerable weight, which has caused large settlements. A thorough evaluation of the soil, the foundation and the structure has been carried out to develop a complex and detailed finite element model. Macro mechanical elements and the direct method have been used to develop the numerical model of the tower in the OpenSees framework. Free ambient vibration tests and non-destructive experiments have been used to calibrate the model. Its dynamic behaviour has been evaluated considering the seismic action suggested by the Spanish Code and those determined through a seismic response analysis, bearing in mind different return periods and considering real ground motions. Finally, the numerical results showed that the effect of the soil and the foundation have a significant impact on the seismic behaviour of the bell tower, amplifying the acceleration and its damage at the top.

Abnormal apparent supershear rupture with discontinuous jumping propagation during the 2023 Türkiye M7.8 earthquake

Earthquake ruptures along a single fault or along a connected system of faults are generally assumed to progress continuously. However, our analysis of the 2023 M7.8 Türkiye earthquake, using finite-fault joint source inversion, uncovered the occurrence of discontinuous rupture jumps. The main fault area adjacent to the splay fault where the earthquake started, and the deeper portion of the northeastern main fault segment exhibited triggered slip before the main rupture front arrived. Through seismic centroid analysis and finite-fault inversion, we estimated apparent rupture speeds within these slip patches reach approximately 6.0 km s-1, exceeding local S-wave velocity. The dynamic triggering mechanism induced the jumping rupture in these areas, resulting in an apparent rupture velocity surpassing the local shear wave velocity. These findings demonstrate the importance of dynamic triggering in adjacent fault systems during large earthquakes, influencing the extent and complexity of rupture propagation.

Sleep Disturbance Caused by Step Changes in Railway Noise Exposure and Earthquakes.

Kyushu Shinkansen and conventional railway lines run parallel in the areas 5 km north of Kumamoto Station (northern area) and 12 km south of the station (southern area). Following the operation of the Kyushu Shinkansen Line in 2011, the adjacent conventional railway line in the north was elevated, a new station was operated in the south, and large earthquakes struck the Kumamoto area from March to April 2016. Sleep disturbances were compared before and after the interventions and earthquakes based on noise source (Shinkansen and conventional railways), area (northern and southern), and house type (detached and apartment) through socio-acoustic surveys from 2011 to 2017. The Shinkansen railway caused significantly less sleep disturbances in detached houses in the north after compared to before the earthquakes, presumably due to more frequent closures of bedroom windows in northern detached houses following the earthquakes. The Shinkansen railway caused significantly more sleep disturbances in apartments in the south after compared to before the earthquakes, presumably because the Shinkansen slowed down immediately after the earthquakes and returned to normal speed during the survey, suddenly increasing the noise exposure. There was no significant difference in the other six cases investigated. Overall, the interventions may not have caused significant differences in sleep disturbances. This article expands on the congress paper by Morihara et al. presented in the "Community Response to Noise" session at the 52nd International Congress and Exhibition on Noise Control Engineering in Makuhari, Japan, organized by the International Institute of Noise Control Engineering.

Did Short‐Term Preseismic Crustal Deformation Precede the 2011 Great Tohoku‐Oki Earthquake? An Examination of Stacked Tilt Records

AbstractThe detection of preslip, occurring hours to days before a large earthquake, using geodetic measurements has been a major focus in earthquake prediction research. A recent study claims to have detected a preseismic signal interpreted as accelerating slip near the hypocenter of the 2011 great Tohoku‐oki earthquake, starting approximately 2 hr before the mainshock. This claim is based on a stacking procedure using GNSS (Global Navigation Satellite System) data. However, a follow‐up study demonstrated that the signal disappeared when specific GNSS noise was corrected. Here we utilize tiltmeter records, independent on GNSS, to check whether the claimed preseismic signal is detected using a similar stacking procedure. Our results show no acceleration‐like deformation from 2 hr before the mainshock. This indicates that no precursory slip exceeded the noise level of the tilt data, and if any preslip occurred, it was less than 5.0 × 1018 Nm in seismic moment.

Near-surface characterization using shear-wave resonances: A case study from offshore Svalbard, Norway

Shear-wave (S-wave) resonances are typically observed when the surficial marine sediments over a rock substrate have relatively low S-wave velocities. We observe these phenomena using ocean-bottom fiber-optic distributed acoustic sensing (DAS) in two subsea fiber-optic telecommunication cables in Svalbard, Norway. Strong seismic energy from sufficiently large earthquakes is required to trigger and enhance the multiple-order modes of S-wave resonances. Here, we use the interpreted S-wave resonance frequencies of the first two modes to determine the thickness and the S-wave velocity of the near-surface low-velocity layer (LVL) beneath the seafloor. In addition, we use existing active P-wave seismic reflection data to determine the LVL thickness and to help build a more accurate S-wave velocity model from the S-wave resonance frequencies. The estimated S-wave velocity varies laterally within the LVL formation. Here, we find that the sediments or deposits with high S-wave velocity presented in the estimated LVL model agree with the distribution of some glacigenic sediments and landforms deposited in the survey area. Therefore, S-wave resonances measured by ocean-bottom DAS can be used to characterize the corresponding near-surface LVLs.

Geofluid behavior prior to the 2018 Hokkaido Eastern Iburi earthquake: insights from groundwater geochemistry

A notable decrease of groundwater Na/K ratios was observed several months before the 2018 Hokkaido Eastern Iburi earthquake (M6.7) at a site approximately 20 km west of the earthquake’s epicenter. To investigate the cause of the decreased Na/K ratios, we analyzed groundwater samples (commercially bottled drinking water) to assess the contribution of deep-derived fluids using Li and Sr isotopic ratios, which are reliable indicators of deep fluid contributions. No pronounced changes in the 7Li/6Li and 87Sr/86Sr ratios were observed; thus, the pre-earthquake decrease of groundwater Na/K ratios did not result from the input of deep-derived fluids. The pre-earthquake decrease in the Na/K ratio observed in this study may instead be related to CO2 influx into the aquifer. The CO2 may have leaked from carbon dioxide capture and storage (CCS), because CCS was in operation near the epicenter of the 2018 Hokkaido Eastern Iburi earthquake. Decreases of the Na/K ratios and increases of the CO2 concentrations in groundwater have been reported before other large earthquakes; thus, CO2 influx into groundwater may be a common phenomenon preceding earthquakes.

Precise relative magnitude measurement improves fracture characterization during hydraulic fracturing

SUMMARY Microseismic monitoring is an important technique to obtain detailed knowledge of in-situ fracture size and orientation during stimulation to maximize fluid flow throughout the rock volume and optimize production. Furthermore, considering that the frequency of earthquake magnitudes empirically follows a power law (i.e. Gutenberg–Richter), the accuracy of microseismic event magnitude distributions is potentially crucial for seismic risk management. In this study, we analyse microseismicity observed during four hydraulic fracture treatments of the legacy Cotton Valley experiment in 1997 at the Carthage gas field of East Texas, where fractures were activated at the base of the sand-shale Upper Cotton Valley formation. We perform waveform cross-correlation to detect similar event clusters, measure relative amplitude from aligned waveform pairs with a principal component analysis, then measure precise relative magnitudes. The new magnitudes significantly reduce the deviations between magnitude differences and relative amplitudes of event pairs. This subsequently reduces the magnitude differences between clusters located at different depths. Reduction in magnitude differences between clusters suggests that some attenuation-related biases could be effectively mitigated with relative magnitude measurements. The maximum likelihood method is applied to understand the magnitude frequency distributions and quantify the seismogenic index of the clusters. Statistical analyses with new magnitudes suggest that fractures that are more favourably oriented for shear failure have lower b-value and higher seismogenic index, suggesting higher potential for relatively larger earthquakes, rather than fractures subparallel to maximum horizontal principal stress orientation.

Deep learning for deep earthquakes: insights from OBS observations of the Tonga subduction zone

SUMMARY Applications of machine learning in seismology have greatly improved our capability of detecting earthquakes in large seismic data archives. Most of these efforts have been focused on continental shallow earthquakes, but here we introduce an integrated deep-learning-based workflow to detect deep earthquakes recorded by a temporary array of ocean-bottom seismographs (OBSs) and land-based stations in the Tonga subduction zone. We develop a new phase picker, PhaseNet-TF, to detect and pick P- and S-wave arrivals in the time–frequency domain. The frequency-domain information is critical for analysing OBS data, particularly the horizontal components, because they are contaminated by signals of ocean-bottom currents and other noise sources in certain frequency bands. PhaseNet-TF shows a much better performance in picking S waves at OBSs and land stations compared to its predecessor PhaseNet. The predicted phases are associated using an improved Gaussian Mixture Model Associator GaMMA-1D and then relocated with a double-difference package teletomoDD. We further enhance the model performance with a semi-supervised learning approach by iteratively refining labelled data and retraining PhaseNet-TF. This approach effectively suppresses false picks and significantly improves the detection of small earthquakes. The new catalogue of Tonga deep earthquakes contains more than 10 times more events compared to the reference catalogue that was analysed manually. This deep-learning-enhanced catalogue reveals Tonga seismicity in unprecedented detail, and better defines the lateral extent of the double-seismic zone at intermediate depths and the location of four large deep-focus earthquakes relative to background seismicity. It also offers new potential for deciphering deep earthquake mechanisms, refining tomographic models, and understanding of subduction processes.

Nowcasting Earthquakes With Stochastic Simulations: Information Entropy of Earthquake Catalogs

AbstractEarthquake nowcasting has been proposed as a means of tracking the change in large earthquake potential in a seismically active area. The method was developed using observable seismic data, in which probabilities of future large earthquakes can be computed using Receiver Operating Characteristic methods. Furthermore, analysis of the Shannon information content of the earthquake catalogs has been used to show that there is information contained in the catalogs, and that it can vary in time. So an important question remains, where does the information originate? In this paper, we examine this question using stochastic simulations of earthquake catalogs. Our catalog simulations are computed using an Earthquake Rescaled Aftershock Seismicity (“ERAS”) stochastic model. This model is similar in many ways to other stochastic seismicity simulations, but has the advantage that the model has only 2 free parameters to be set, one for the aftershock (Omori‐Utsu) time decay, and one for the aftershock spatial migration away from the epicenter. Generating a simulation catalog and fitting the two parameters to the observed catalog such as California takes only a few minutes of wall clock time. While clustering can arise from random, Poisson statistics, we show that significant information in the simulation catalogs arises from the “non‐Poisson” power‐law aftershock clustering, implying that the practice of de‐clustering observed catalogs may remove information that would otherwise be useful in forecasting and nowcasting. We also show that the nowcasting method provides similar results with the ERAS model as it does with observed seismicity.

Evidence for an Imbricated Lower Crust and Its Role in Accommodating Crustal Shortening in Sikkim Himalaya

AbstractGeometrical heterogeneity of the subducting Indian continental crust along the Himalaya‐Tibet collision zone remains enigmatic. Mass budget estimates describing shortening across the orogen are partly derived from observations made from seismic imaging of the deep earth. Here, using data from 38 broadband seismic stations covering Sikkim Himalaya, we produce high resolution seismic images in order to fill crucial gaps in our understanding of the evolution of Himalayan collision zone. We used 12,288 high quality receiver functions computed using waveforms of earthquakes having magnitude >5.5 in the distance range of 30°–100°. Our results reveal a highly imbricated and heterogeneous crust beneath Sikkim Himalaya. The Main Himalayan Thrust (MHT) responsible for large scale earthquakes in the Himalayan collision zone is not so distinct in the migrated images, but intermittent. A dominant cluster of earthquakes at shallower depths is associated with the MHT, marked by negative amplitude arrivals. The Moho is found to be gently dipping, reaching depths of ∼60 km beneath the Higher Himalaya compared to ∼40 km in the Himalayan foredeep. Interestingly, the Moho in this part of Himalaya has offsets and overlapping segments, indicating crustal imbrication in response to active shortening. Clusters of lower crustal earthquakes coincide with the junction of offsets in the Moho.

Event-specific ground motion anomalies highlight the preparatory phase of earthquakes during the 2016–2017 Italian seismicity

Although physical models are improving our understanding of the crustal processes that lead to large earthquakes, observing their preparatory phases is still challenging. We show that the spatio-temporal evolution of the ground motion of small magnitude earthquakes can shed light on the preparatory phase of three main earthquakes that occurred in central Italy between 2016 and 2017. We analyze systematic deviations of peak ground accelerations generated by each earthquake from the values predicted by a reference ground motion model calibrated for background seismicity and refer to such deviations as event-specific ground motion anomalies (eGMAs). The eGMA temporal behavior indicates that during the activation phase of the main earthquakes, the ground shaking level deviates, positively or negatively, from the values expected for the background seismicity. eGMA can be exploited as beacons of stress change and help to monitor the mechanical state of the crust and the nucleation of large earthquakes.

Evaluation of the b Maps on the Faults of the Major (M > 7) South California Earthquakes

AbstractWe use the Godano et al. (2022, https://doi.org/10.1029/2021ea002205) method for evaluating the b maps of the faults associated with the largest earthquakes M ≥ 7.0 that occurred in California. The method allows an independent evaluation of the b parameter, avoiding the overlap of the cells and the omission of some earthquakes, while keeping all the available information in the catalog. We analyzed four large earthquakes: Landers, Hector Mine, Baja California, and Searles Valley. The maps obtained confirm that the b value can be considered as a strain meter and allow us to elucidate the presence of barriers, such as obstacles to the propagation of the fracture, on the fault of the analyzed earthquakes. A further estimated parameter is the time window during which aftershocks occur in the cell, Δt. This quantity is very useful for a better definition of the aftershock generation mechanism. It reveals where the stress is released in a short time interval and how the complexity of the faulting process controls the occurrence of aftershocks on the fault, and also the duration of the entire sequence.

A Comprehensive Approach to Quantitative Risk Assessment of Rockfalls on Buildings Using 3D Model of Rockfall Runout

Rockfalls are incidents of nature that take place when rocks or boulders break from a steep slope and fall to the ground. They can pose considerable threats to buildings placed in high-risk zones. Despite the fact that the impact of a rockfall on a building can cause structural and non-structural damage, few studies have been undertaken to investigate the danger associated with this event. Most of these studies indicated that the risk resulting from rockfall hazards is hard to forecast and assess. A comprehensive quantitative risk assessment approach for rockfalls on buildings is developed and described in this paper and applied for the Mtein village in Mount Lebanon. This method employs a 3D model to simulate the rockfall trajectories using a combination of digital elevation data, field surveys, and orthorectified aerial photographs. The spatial and temporal probability of rockfalls were evaluated using the analysis of historical data in two triggering-factor scenarios: earthquake and precipitation. The findings show that, during the period of 1472 years between the years 551 (the first observed large earthquake in Lebanon) and the current year of the study (2023), the temporal probability will potentially be equal to 0.002 and 0.105 in the cases of earthquake- and rainfall-triggered rockfalls, respectively, while the maximal damage values are expected to be 232 USD and 10,511 USD per year, respectively. The end result is a final map presenting the risk values assigned to each building that could be damaged by rockfalls.

Coseismic and Early Postseismic Deformation of the 2024 Mw7.45 Noto Peninsula Earthquake

AbstractAn unexpected Mw7.45 earthquake struck the Noto Peninsula on 1 January 2024, preceded by several long‐living earthquake swarms, providing a valuable opportunity to study seismic and aseismic slips, as well as their interactions. We derived coseismic and 19‐day postseismic slip distributions by inverting co‐ and post‐seismic displacements from Global Navigation Satellite System (GNSS) data. The inverted coseismic slip distribution shows two slip patches, with a maximum slip of ∼4 m. The early postseismic afterslip is 0.1–0.25 m within coseismic slip asperity and 0.1–0.6 m northward of the rupture area. The afterslip within the rupture area is accompanied by numerous aftershocks and coincides with a ∼6 MPa stress drop, suggesting that aftershocks are likely driven by the afterslip. The pattern of poroelastic rebound implies a potential effect of fluid flow on aftershock triggering. This study sheds lights on the intricate interplay between seismic and aseismic processes following large earthquakes.