Ground Shaking Research Articles

Joint earthquake ruptures of the San Andreas and San Jacinto faults, California, USA

Abstract Large, multi-fault earthquakes increase the threat of strong ground shaking and reshape the probability of future events across a system of faults. Fault junctions act as conditional barriers, or earthquake gates, that stop most earthquakes but permit junction-spanning events when stress conditions are favorable. Constraining the physical conditions that favor multi-fault earthquakes requires information on the frequency of isolated events versus events that activate faults through the junction. Measuring this frequency is challenging because dating uncertainties limit correlation of paleoseismic events at different faults, requiring a direct approach to measuring rupture through an earthquake gate. We show through documentation and finite-element modeling of secondary fault slip that co-rupture of the San Andreas and San Jacinto faults (California, USA) through the Cajon Pass earthquake gate occurred at least three times in the past 2000 yr, most recently in the historic 1812 CE earthquake. Our models show that gate-breaching events taper steeply and halt abruptly as they transfer slip between faults. Comparison to independent chronologies shows that 20%–23% of earthquakes on the San Andreas and the San Jacinto faults are co-ruptures through Cajon Pass.

Mapping the Potential Liquefaction Area in Yogyakarta City Based on Ground Shear Strain Data

The appearance of liquefaction phenomena in some places in Yogyakarta city due to the 2006 earthquake indicates that the sediment in this area has a high potential to liquefy. Three main factors that caused liquefaction are ground shaking, lithological conditions, and groundwater depth. This study aims to investigate one of the three factors i.e ground shaking. For this purpose, the ground shear strain (GSS) data were analyzed for mapping the potential liquefaction area in Yogyakarta city. They were calculated from the seismic vulnerability index and PGA. The seismic vulnerability index was analyzed from a microtremor single station data recorded in 110 sites while PGA was calculated using a reference of the 2006 earthquake. The GSS value in the study area is at a range of 2.0 × 10 −4 to 5.8 × 10 −3 . In this range, the soils begin to be elastic-plastic so that they are susceptible to be fracture and settlement. The high GSS correlates with the location of the liquefaction due to the 2006 earthquake. The liquefaction potential map was obtained by comparing the GSS with liquefaction sites. The high liquefaction potential is located in the southern part of Yogyakarta city covering Mantrijeron, Mergangsan, Pakualaman, Umbulharjo, and Kotagede districts.

Enhancement of convolutional neural network for urban environment parking space classification

BACKGROUND AND OBJECTIVES: Soil or rock properties where buildings are situated play an important role in the ground shaking caused by an earthquake. The highly populated Banda Aceh city in the northernmost Sumatra is flanked by two active faults, the Seulimeum and the Aceh segment. Therefore, it is crucial to investigate the subsurface characteristics of the region to reduce the earthquake risk as there was no regional study has been conducted so far.METHODS: Characteristics of the soil or rock of the subsurface were derived from various seismic parameters. The seismic microtremors were recorded at 36 sites covering the highly populated city and the two active faults. The spatial autocorrelation method was used to obtain a dispersion curve based on the relationship between seismic frequencies and phase velocity from triangular geophones array to determine the shear wave velocity of the subsurface layer. The seismic amplification, dominant frequency and vulnerability value at each measurement point were measured using the horizontal-to-vertical spectral ratio method. The maps of velocity structure and HVSR parameters were generated from the interpolation of those seismic parameters.FINDING: Based on the variation of the four geophysical parameters: shear wave velocity, seismic amplification, dominant frequency, and seismic vulnerability, the study area can be clustered into five different groups: I) Banda Aceh, II) Jantho, III) Krueng Raya, IV) Lhoknga-Lhoong, and V) Seulawah, which classify the different types of rocks. The classification of soil properties from the combination of shear wave and horizontal-to-vertical spectral ratio data correlates with the geology of the study area.CONCLUSION: The Banda Aceh city, flanked by the two active faults, is characterized by low shear wave velocity and high amplification because the city stands on the sedimentary basin; thus, it requires a detailed investigation prior to constructing infrastructures. The other clusters are located on the relatively less vulnerable areas, indicated by moderate shear wave velocity and moderate to low seismic vulnerability indexes. The joint analysis shows that the combination of physical properties, including the shear wave velocity, seismic amplification, and dominant frequency, can be used to investigate lithology and seismic vulnerability into a specific cluster. The research results are essential for hazard mitigation and can be used for disaster risk management by the local government. A detailed investigation with denser measurement points needs to be conducted to comprehensively describe the types of rocks in Banda Aceh and its surrounding.

System Response of an Interlayered Deposit with Spatially Preferential Liquefaction Manifestations

The Canterbury Earthquake Sequence produced a spatial pattern of liquefaction-induced surface ejecta at an open field along Palinurus Road in Christchurch, New Zealand, that would not be expected based on simplified liquefaction evaluation procedures. Half the site discharged sand boils and the other half did not. Two-dimensional fully-coupled nonlinear dynamic analyses (NDAs) were performed to examine why simplified one-dimensional liquefaction vulnerability indices (LVIs) overestimated liquefaction manifestations at this site for the 2010 Darfield and 2011 Christchurch earthquakes and did not distinguish between areas with and without surface ejecta. The NDAs use the PM4Sand and PM4Silt constitutive models for sand-like and clay-like portions of the subsurface, respectively, within the Fast Lagrangian Analysis of Continua (FLAC) finite-difference program. Material parameters are obtained from in situ geophysical and cone penetration test (CPT) data. A sensitivity study is performed to assess the influence of (1) representative soil property selections and the use of a CPT inverse filtering procedure to correct for thin-layer and transition zone effects, (2) ground motions developed by two distinct methods (i.e., recordings and physics-based simulations), and (3) model assumptions affecting diffusion during reconsolidation. Ground deformations and flow patterns during and after ground shaking are examined. The results provide insights on how stratigraphic details and other factors can affect the system response and dictate the degree and extent of liquefaction surface manifestations.

Assessment of Perception on Disaster Proneness of Lembang Fault in District of Cisarua, West Java Indonesia

The Lembang Fault is a major fault located at the northern Bandung. This fault has a high disaster risk, including ground shaking, surface rupture, and possible landslides or liquefaction. This fault can cause earthquakes of 6.5-7 magnitude, making 8 million people in four Regencies and Cities around West Bandung Regency, Cimahi City, Bandung City and Bandung Regency exposed to major disaster risk. This research focuses on assessing the Perception of Disaster Proneness of the Lembang Fault in the District of Cisarua, West Java, Indonesia. This research was conducted using a case study and deductive-qualitative approach. In addition, this research was carried out by combining engineering and social research methodologies. The survey location point is determined based on hazard data (Peak Ground Acceleration data), vulnerability data (covering building density, slope, curvature, soil character, distance from faults, etc.) and population density data. This study indicates that the public’s perception of the disaster in the Lembang Fault is very subjective. How they act is based on experience or based on their beliefs. Therefore, an essential part of this research is assessing and measuring the community’s perception of the Lembang Fault towards disasters that may arise. The government must make serious efforts to convey that the disaster in the Lembang fault is much bigger and can happen at any time. Therefore, building resilient communities that genuinely understand the dangers of living in disaster-prone areas is essential.

A New Smoothed Seismicity Approach to Include Aftershocks and Foreshocks in Spatial Earthquake Forecasting: Application to the Global Mw ≥ 5.5 Seismicity

Seismicity-based earthquake forecasting models have been primarily studied and developed over the past twenty years. These models mainly rely on seismicity catalogs as their data source and provide forecasts in time, space, and magnitude in a quantifiable manner. In this study, we presented a technique to better determine future earthquakes in space based on spatially smoothed seismicity. The improvement’s main objective is to use foreshock and aftershock events together with their mainshocks. Time-independent earthquake forecast models are often developed using declustered catalogs, where smaller-magnitude events regarding their mainshocks are removed from the catalog. Declustered catalogs are required in the probabilistic seismic hazard analysis (PSHA) to hold the Poisson assumption that the events are independent in time and space. However, as highlighted and presented by many recent studies, removing such events from seismic catalogs may lead to underestimating seismicity rates and, consequently, the final seismic hazard in terms of ground shaking. Our study also demonstrated that considering the complete catalog may improve future earthquakes’ spatial forecast. To do so, we adopted two different smoothed seismicity methods: (1) the fixed smoothing method, which uses spatially uniform smoothing parameters, and (2) the adaptive smoothing method, which relates an individual smoothing distance for each earthquake. The smoothed seismicity models are constructed by using the global earthquake catalog with Mw ≥ 5.5 events. We reported progress on comparing smoothed seismicity models developed by calculating and evaluating the joint log-likelihoods. Our resulting forecast shows a significant information gain concerning both fixed and adaptive smoothing model forecasts. Our findings indicate that complete catalogs are a notable feature for increasing the spatial variation skill of seismicity forecasts.

Effects of pounding on the behavior of reinforced concrete frame structures in seismic zone 2B

Pounding between adjacent buildings is a common phenomenon which can be observed during moderate to high ground shakings that can result in structural damage and even loss of life. As this phenomenon is related to the life safety, therefore, it is imperative to consider it in the modelling stage of structural analysis and design. The current study is intended to evaluate, numerically, the effect of pounding phenomenon in RC frame structures. Three dimensional models of two hypothetical buildings are analyzed by subjecting to three ground acceleration histories that are scaled and matched with BCP-SP07 design spectrum. The analysis results such as inter storey drift, maximum displacement, pounding forces and its effects on bending moment, axial forces, shear and torsional forces in structural members are compared. The results show that pounding forces decrease with increase in gap size and are dominant in top five stories with maximum force at the top floor level. Pounding increase displacement up to 2 times and acceleration up to 240 times as compared to without pounding case. Pounding increase the axial forces up to 250 times and bending moment up to 2 time in the beams parallel to colliding forces. Similarly, the shear forces and torsional moments are almost doubled as a result of pounding. Finally, a 20 storey building consists of four blocks separated by 3-inch expansion joints is modelled combinedly in Etabs and analyzed to see the effect of pounding. Based on the results it is concluded that pounding must be considered at modelling stage of the design to account for the forces induced in the structural members.

Seismic Response Control of Elevated Water Tank using Base Isolation: A Review

Earthquake events are not something which can be avoidable. The Indian subcontinent has a background marked by devasting quakes. Quakes are generally caused when the stone underground out of nowhere breaks along an issue. Ground shake is caused by seismic waves due to sudden release of energy. The Centre of earthquake vibration is known as epicentre. Due to earthquake millions of lives are lost which can never be affordable. Most of the structures are subjected to vibrations; it causes destruction of country’s infrastructure. In the recent earthquakes many well designed concrete structures have been severely damaged or collapsed. To protect structures from response reduction of structures and important harm under such serious earthquakes has become a vital theme in structural engineering. In this investigation, we evaluated seismic performance of staging system of elevated water storage tank with or without Base Isolation by using SAP2000. From this examination the powers following up on elevated water tank because of seismic powers are determined for zone IV.

Exploring Basin Amplification within the Reno Metropolitan Area in Northern Nevada Using a Magnitude 6.3 ShakeOut Scenario

ABSTRACTThe Reno metropolitan area (located within the Truckee Meadows in northern Nevada) is subjected to significant seismic risk, primarily resulting from the region’s proximity to the Mount Rose fault system and the urban area’s presence within a large, thin (<1 km thick) sedimentary basin. Numerous paleoseismic studies have shown the Mount Rose fault system has a history of producing large Holocene earthquakes. To help explore this hazard, we used SW4, a physics-based wave-equation modeling tool, to develop the Reno ShakeOut Scenario. The scenario uses a grid with a minimum spacing of 20 m with eight points per minimum wavelength to perform a full 3D simulation for a potential magnitude 6.3 earthquake within the Mount Rose fault system. The calculation assumes a minimum shear-wave velocity (VSmin) of 500 m/s and is accurate up to 3.125 Hz. Results indicate that there is a potential for widespread and variable ground shaking at modified Mercalli intensity (MMI) magnitudes between VII and VIII (very strong to severe ground shaking), with some areas achieving violent (IX and X) motions. Distributions of high shaking are controlled by proximity to the rupture, geotechnical shear-wave velocity, topography; and significantly, basin geometry. Comparisons between SW4 peak ground velocity (PGV) computations, and PGV estimates calculated from the Campbell and Bozorgnia empirical ground-motion model emphasize the degree to which very thin basins may result in greater hazard than is currently predicted. This information helps improve our understanding of regional risk by highlighting these significant basin effects and the local variability that is likely to occur with any large seismic event.

Seismic vulnerability modelling of building portfolios using artificial neural networks

ABSTRACTThe incorporation of machine learning (ML) algorithms in earthquake engineering can improve existing methodologies and enable new frameworks to solve complex problems. In the present study, the use of artificial neural networks (ANNs) for the derivation of seismic vulnerability models for building portfolios is explored. Large sets of ground motion records (GMRs) and structural models representing the building stock in the Balkan region were used to train ANNs for the prediction of structural response, damage and economic loss conditioned on a vector of ground shaking intensity measures. The structural responses and loss ratios (LRs) generated using the neural networks were compared with results based on traditional regression models using scalar intensity measures in terms of efficiency, sufficiency, bias and variability. The results indicate a superior performance of the ANN models over traditional approaches, potentially allowing a greater reliability and accuracy in scenario and probabilistic seismic risk assessment.

Ground motion models for shallow crustal and deep earthquakes in Hawaii and analyses of the 2018 M 6.9 Kalapana sequence

The damaging 4 May 2018 M 6.9 Kalapana earthquake and its aftershocks have provided the largest suite of strong motion records ever produced for an earthquake sequence in Hawaii exceeding the number of records obtained in the deep 2006 M 6.7 Kiholo Bay earthquake. These records provided the best opportunity to understand the processes of strong ground shaking in Hawaii from shallow crustal (< 20 km) earthquakes. There were four foreshocks and more than 100 aftershocks of M 4.0 and greater recorded by the seismic stations. The mainshock produced only a modest horizontal peak ground acceleration (PGA) of 0.24 g at an epicentral distance of 21.5 km. In this study, we evaluated the 2018 strong motion data as well as previously recorded shallow crustal earthquakes on the Big Island. There are still insufficient strong motion data to develop an empirical ground motion model (GMM) and so we developed a GMM using the stochastic numerical modeling approach similar to what we had done for deep Hawaiian (>20 km) earthquakes. To provide inputs into the stochastic model, we performed an inversion to estimate kappa, stress drops, Ro, and Q(f) using the shallow crustal earthquake database. The GMM is valid from M 4.0 to 8.0 and at Joyner–Boore (RJB) distances up to 400 km. Models were developed for eight VS30 (time-averaged shear-wave velocity in the top 30 m) values corresponding to the National Earthquake Hazards Reduction Program (NEHRP) site bins: A (1500 m/s), B (1080 m/s), B/C (760 m/s), C (530 m/s), C/D (365 m/s), D (260 m/s), D/E (185 m/s), and E (150 m/s). The GMM is for PGA, peak horizontal ground velocity (PGV), and 5%-damped pseudo-spectral acceleration (SA) at 26 periods from 0.01 to 10 s. In addition, we updated our GMM for deep earthquakes (>20 km) to include the same NEHRP site bins using the same approach for the crustal earthquake GMM.

Results of recording sonic waves by seismic stations in the territory of Karelia

In spite of a relatively low seismic activity level, the detailed study of Karelia is not only of theoretical, scientific interest, but is also of practical value which has increased markedly because there are big industrial complexes, gas pipelines and hydrotechnical facilities in the region. The results of recording sonic waves of various nature by stationary and mobile seismic stations are presented. For the observation period 2000—2020 an array of seismic data has been accumulated. In order to correctly understand the nature of the signals under consideration, it should be noted that North Karelia is known to belong to seismic regions, where 5-point earthquakes have taken place earlier. They were distinguished from earthquakes generated by frost cracking by both visual and instrumental data. They are known throughout Fennoscandia. This group comprises both tremors during frost cracking of the soil, primarily with a sharp change in temperature, and frost cracking of ice in inland water bodies. To decide on the nature of ground shaking, it is necessary to pay attention to such signs as the limited area of oscillations and the nature of the wave record. As a result of seismic monitoring of Karelia, the following frost quakes were also recorded: the passage of the bolidi, the take-off of an aircraft, blasting operations during the disposal of ammunition and mining in the immediate vicinity of residential areas and industrial facilities. A wide range of possible sources and examples of sound waveforms are shown. The data obtained indicate the possibility of some shocks with a force of up to 4ѕ5 points in the immediate vicinity of the place of registration, what should be considered in the routine processing of seismic events and seismic hazard assessment in the southeastern Fennoscandian Shield.

STEPS: Slip Time Earthquake Path Simulations Applied to the San Andreas and Toe Jam Hill Faults to Redefine Geologic Slip Rate Uncertainty

AbstractGeologic slip rates are a time‐averaged measurement of fault displacement calculated over hundreds to million‐year time scales and are a primary input for probabilistic seismic hazard analyses, which forecast expected ground shaking in future earthquakes. Despite their utility for seismic hazard calculations, longer‐term geologic slip rates represent a time‐averaged measure of the tempo of strain release and do not measure variability across earthquake cycles. We have developed a numerical approach called STEPS (Slip Time Earthquake Path Simulations), which is built upon field‐based observations and explicitly incorporates realistic variations in displacement per event and variability in the recurrence interval between earthquakes. The STEPS approach, which simulates strain release through time, relies on representing earthquake cycles as stairsteps, rather than straight‐line paths, connecting per earthquake time‐displacement coordinates. We simulate earthquake histories based on these input constraints using two examples: the Carrizo section of the San Andreas fault and the Toe Jam Hill fault of the Seattle fault zone. We find that modeled slip rate distributions agree with slip rates reported for the sites of interest by the original investigators, while providing a slip rate distribution that reflects the variability of earthquake frequency and displacement. The STEPS approach provides an estimate of fault slip rate uncertainty based on a synthetic suite of plausible time‐displacement paths resulting from individual earthquakes, rather than measurement uncertainties associated with offset features. When considering this simulated earthquake behavior between measurements, the uncertainty associated with earthquake paths is greater than that calculated by the long‐term rate.

Neogene-Quaternary tectonic regime and macroseismic observations in the Tyrnavos-Elassona broader epicentral area of the March 2021, intense earthquake sequence

On March 3, 2021, a strong (Mw6.3) earthquake occurred near the towns of Tyrnavos and Elassona. One day later (March 4), a second strong (Mw6.0) earthquake occurred just a few kilometres toward the WNW. The aftershock spatial distribution and the focal mechanisms revealed NW-SE-striking normal faulting. The focal mechanisms also revealed a NE-SW oriented extensional stress field, different from the orientation we knew so far (ca. N-S). The magnitude and location of the two strongest shocks, and the spatiotemporal evolution of the sequence, strongly suggest that two adjacent fault segments were ruptured respectively. The sequence was followed by several coseismic ground deformational phenomena, such as landslides/rockfalls, liquefaction and ruptures. The landslides and rockfalls were mostly associated with the ground shaking. The ruptures were observed west of the Titarissios River, near to the Quaternary faults found by bore-hole lignite investigation. In the same direction, a fault scarp separating the alpidic basement from the alluvial deposits of the Titarissios valley implies the occurrence of a well-developed fault system. Some of the ground ruptures were accompanied by extensive liquefaction phenomena. Others cross-cut reinforced concrete irrigation channels without changing their direction. We suggest that this fault system was partially reactivated, as a secondary surface rupture, during the sequence as a steeper splay of a deeper low-to-moderate angle normal fault.

Camera motion-induced systematic errors in stereo-DIC and speckle-based compensation method

Stereo-digital image correlation (stereo-DIC) is now a standard technique for determination of the mechanical properties of materials and structures. In stereo-DIC, cameras are assumed to be motionless after camera calibration, so the three-dimensional (3D) reconstruction can be implemented using pre-calibrated parameters. However, this assumption is not true in some situations, such as drop test, seismic shaking table test and non-laboratory environment. Due to the presence of ground shaking or wind blowing, it's almost impossible to avoid camera motion in these experiments even if mechanical fixing is adopted. Camera motion during the experiment can undoubtedly introduce significant errors on measured results. Generally, camera motion can be divided into pair motion and relative motion. The influence of these two kinds of motion on stereo-DIC measurement is different and worth of separate study. Keep this in mind, in this paper, the influence of camera motion on stereo-DIC is investigated and the effects of pair motion and relative motion are examined separately using precisely controllable simulated experiments. Specifically, by integrating into the stereo matching, the speckle-based compensation method for relative motion is proposed and the accuracy of the compensation methods is analyzed in detail. The reduction of camera motion-induced systematic errors will be helpful for the further applications of stereo-DIC in non-laboratory environments and engineering fields.

Real-Time Prediction of Impending Ground Shaking: Review of Wavefield-Based (Ground-Motion-Based) Method for Earthquake Early Warning

Earthquake early warning (EEW) systems aim to provide advance warning of impending ground shaking, and the technique used for real-time prediction of shaking is a crucial element of EEW systems. Many EEW systems are designed to predict the strength of seismic ground motions (peak ground acceleration, peak ground velocity, or seismic intensity) based on rapidly estimated source parameters (the source-based method), such as hypocentral location, origin time, magnitude, and extent of fault rupture. Recently, however, the wavefield-based (or ground-motion-based) method has been developed to predict future ground motions based directly on the current wavefield, i.e., ground motions monitored in real-time at neighboring sites, skipping the process of estimation of the source parameters. The wavefield-based method works well even for large earthquakes with long duration and huge rupture extents, highly energetic earthquakes that deviate from standard empirical relations, and multiple simultaneous earthquakes, for which the conventional source-based method sometimes performs inadequately. The wavefield-based method also enables prediction of the ongoing seismic waveform itself using the physics of wave propagation, thus providing information on the duration, in addition to the strength of strong ground motion for various frequency bands. In this paper, I review recent developments of the wavefield-based method, from simple applications using relatively sparse observation networks to sophisticated data assimilation techniques exploiting dense networks.

Impacts on catastrophe risk assessments from multi-segment and multi-fault ruptures in the UCERF3 model

The Uniform California Earthquake Rupture Forecast Version 3 (UCERF3) relaxes fault segmentation, allowing multi-segment and multi-fault ruptures through fault-to-fault “jumps,” with lengths up to ∼1200 km along the San Andreas Fault. Local faults are also highly interconnected, including ruptures on the order of hundreds of kilometers. These prescribed long ruptures did not exist in older models. Longer ruptures produce larger aggregate loss estimates for geographically dispersed assets (portfolios) due to the wider areas that are affected by strong ground shaking. In this study, we model probabilistic earthquake losses of a hypothetical state-wide building portfolio in California. We develop risk deaggregation methods to identify multi-segment and multi-fault ruptures that contribute significantly to high portfolio-wide risks. Three risk measures that are commonly used in risk management decisions are examined: Average Annual Loss (AAL), Return Period Loss (RPLα), and Tail Conditional Expectation (TCEα), for an annual exceedance probability “α,” or corresponding return period “1/α.” Our results show that while the super long ruptures (>500 km) contribute modestly (∼7%) to the portfolio AAL estimate, they contribute more significantly to portfolio catastrophe risk estimates. Specifically, at a 250 year return period, these long ruptures contribute about 26% and 32% to RPL250 and TCE250 estimates, respectively. At a 500-year return period, the corresponding contributions reach about 35% and 39%. Ruptures that connect complex fault systems are also found to be highly influential to estimated portfolio risks. At a 500-year return period, a mere six rupture groups contribute nearly 70% to the RPL500 estimate. Due to the importance of the UCERF3 model to many risk management and public policy decisions, a critical examination of the limit and uncertainty of fault connectivity and rupture lengths of future earthquakes, as well as their impacts on catastrophe risk assessments, is warranted in future model updates.

Survey of Fragile Geologic Features and Their Quasi-Static Earthquake Ground-Motion Constraints, Southern Oregon

ABSTRACTFragile geologic features (FGFs), which are extant on the landscape but vulnerable to earthquake ground shaking, may provide geological constraints on the intensity of prior shaking. These empirical constraints are particularly important in regions such as the Pacific Northwest that have not experienced a megathrust earthquake in written history. Here, we describe our field survey of FGFs in southern Oregon. We documented 58 features with fragile geometric characteristics, as determined from field measurements of size and strength, historical photographs, and light detection and ranging point clouds. Among the surveyed FGFs, sea stacks have particular advantages for use as ground-motion constraints: (1) they are frequently tall and thin; (2) they are widely distributed parallel to the coast, proximal to the trench and the likely megathrust rupture surface; and (3) they are formed by sea cliff retreat, meaning that their ages may be coarsely estimated as a function of distance from the coast. About 40% of the surveyed sea stacks appear to have survived multiple Cascadia megathrust earthquakes. Using a quasi-static analysis, we estimate the minimum horizontal ground accelerations that could fracture the rock pillars. We provide context for the quasi-static results by comparing them with predictions from kinematic simulations and ground-motion prediction equations. Among the sea stacks old enough to have survived multiple megathrust earthquakes (n = 16), eight yield breaking accelerations lower than the predictions, although they generally overlap within uncertainty. FGFs with the lowest breaking accelerations are distributed uniformly over 130 km of coastline. Results for inland features, such as speleothems, are in close agreement with the predictions. We conclude that FGFs show promise for investigating both past earthquake shaking and its spatial variability along the coasts of Oregon and Washington, where sea stacks are often prevalent. Future work can refine our understanding of FGF age and evolution.

Fragility assessment of tunnels in soft soils using artificial neural networks

Recent earthquakes have shown that tunnels are prone to damage, posing a major threat to safety and having major cascading and socioeconomic impacts. Therefore, reliable models are needed for the seismic fragility assessment of underground structures and the quantitative evaluation of expected losses. Based on previous researches, this paper presented a probabilistic framework based on an artificial neural network (ANN), aiming at the development of fragility curves for circular tunnels in soft soils. Initially, a two-dimensional incremental dynamic analysis of the nonlinear soil-tunnel system was performed to estimate the response of the tunnel under ground shaking. The effects of soil-structure-interaction and the ground motion characteristics on the seismic response and the fragility of tunnels were adequately considered within the proposed framework. An ANN was employed to develop a probabilistic seismic demand model, and its results were compared with the traditional linear regression models. Fragility curves were generated for various damage states, accounting for the associated uncertainties. The results indicate that the proposed ANN-based probabilistic framework can results in reliable fragility models, having similar capabilities as the traditional approaches, and a lower computational cost is required. The proposed fragility models can be adopted for the risk analysis of typical circular tunnel in soft soils subjected to seismic loading, and they are expected to facilitate decision-making and risk management toward more resilient transport infrastructure.

Hydrological control shift from river level to rainfall in the reactivated Guobu slope besides the Laxiwa hydropower station in China

Landslides are common geohazards associated with natural drivers such as precipitation, land degradation, toe erosion by rivers and wave attack, and ground shaking. On the other hand, human alterations such as inundation by water impoundment or rapid drawdown may also destabilize the surrounding slopes. The Guobu slope is an ancient rockslide on the banks of the Laxiwa hydropower station reservoir (China), which reactivated during the reservoir impoundment in 2009. We extracted three-dimensional surface displacements with azimuth and range radar interferometry using European Space Agency's Copernicus Sentinel-1 and German Aerospace Center's TerraSAR-X data during 20152019. The upper part of the Guobu rockslide is characterized by toppling and is mostly subsiding with maximum rates over 0.4 m/yr and 0.7 m/yr in the vertical and horizontal directions, respectively. During filling of the reservoir prior to 2014, there was a long-wavelength in-phase response between rising reservoir level and GPS-observed increased slope movements. After the reservoir water level stabilized from 2015 to 2019, the slide movement became seasonal and we see a correlation between rainfall and landslide movement. These observations suggest that the slide motion is now primarily controlled by rainfall. The spatiotemporal landslide displacements allow us to estimate the hydraulic diffusivity of the rock mass, to be on the order (~1.05 × 10‐7 m2/s) and the thickness of the moving rock mass (~200 m). Our results demonstrate that InSAR is a useful tool for monitoring the rockslide movement as a function of seasonal precipitation.