Characteristics Of Strong Ground Motions Research Articles

Duration Characteristics of Strong Ground Motions Recorded during the 6 February 2023 M 7.8 Pazarcık, Kahramanmaraş, Türkiye, Earthquake

Abstract The seismograms recorded at a total of 71 strong ground-motion stations (SGMS) located within 100 km of the fault rupture were used to investigate the durational variability observed during the 6 February 2023 M 7.8 Pazarcık, Kahramanmaraş, Türkiye, earthquake. More specifically, significant duration (D) and equivalent number of uniform stress cycles (N) estimated using these accelerograms were compared with the ones predicted by Cetin et al. (2021) and Davatgari-Tafreshi and Bora (2023) models, respectively. To facilitate the comparisons, residuals were estimated and presented with reference to (1) SGMS’ geographical locations; (2) recorded peak ground acceleration (PGA) intensities; (3) distance to the fault rupture, or RJB; (4) site stiffness; and (5) angular orientation of the stations relative to the fault rupture. The assessment results reveal that during the Pazarcık event the duration parameters of D5−75, D5−95, and N were recorded as 23 s, 40 s, and 25 cycles, respectively, on average. Hatay and Kahramanmaraş emerge as the metropolitan cities with the highest PGA intensities, coupled with above-the-average significant durations. A negative correlation is evident between the duration and PGA intensity levels for stations located on the Anatolian side of the rupture, particularly pronounced for the significant duration parameters. The N, D5−75, and D5−95 values appear to be unaffected by RJB distances within 10 km, after which they exhibit an increasing trend. The significant durations were evaluated to be longer at softer soil sites. As the azimuth angle θ increases, D and N were observed to increase.

Effect of site specific soil characteristics on the nonlinear ground response analysis and comparison of the results with equivalent linear analysis

Damages occurring during earthquakes may vary depending on the ground conditions in which the earthquake waves pass, the magnitude of the earthquake, the focal depth of the shaking and as well as the structural characteristics. Regional seismicity, ground movement and behavior of local soil conditions are important in earthquake-resistant building designs. Local site conditions consist of the layering, bedrock depth, and dynamic and topographic characteristics of soil that alter the bedrock waves through the soil profile during an earthquake. The change occurs in terms of amplitude, frequency and the time when the peak happens during the wave propagation. This initiates a big difference between the surface and bedrock motion. The behavior of the soil under cyclic loads resulting from seismic action is non-linear. This study aims to demonstrate the effects of strong ground motion by taking into account the nonlinear behavior of the soil layers. In addition, the results obtained from the equivalent linear and non-linear methods were compared. The results of the study showed that the characteristics of soil layers and strong ground motion (frequency content and duration) significantly affect the field response analysis and generally larger spectral parameters (about %20) have been obtained with the equivalent linear method compared to the nonlinear behavior. Finally, empirical models to estimate the soil amplification reflect different compared to the site specific analysis.

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

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

Regional offshore ground motion prediction model from a referenced empirical approach: A case study in the Japan Trench area

With increasing resource exploitation and engineering construction offshore, the seismic safety of offshore structures has received attention from researchers and designers, and an offshore ground motion prediction model (GMPM) can be used to estimate the possible earthquake response of structures and provide the foundation for seismic fortification of structures. Because there are few strong motion records recorded by offshore stations, there are insufficient empirical data in the magnitude-distance range to directly develop a GMPM using empirical regression techniques. To develop a reliable GMPM for data-poor offshore regions, we used a referenced empirical approach based on an onshore empirical prediction model. We collected 2605 records from 138 crustal earthquake events, 2669 records from 125 slab earthquake events and 5693 records from 267 interface earthquake events recorded by S-net stations. We used the existing Japanese onshore GMPM as a reference model. Then, we analyzed the residuals of the reference model for offshore data and calculated its adjustment factors. Finally, we developed a GMPM for the Japan Trench area and compared it with the existing onshore models. The proposed model fit the data subsets at hypocentral distances of 20–300 km reasonably well. There were different spectral accelerations (SAs) for different source types, with considerably larger SAs for short periods of offshore motions from crustal events than for the motions from the other two types, and the difference becomes more obvious with the increase of magnitude. At short periods, the SAs of the offshore motions from slab events were slightly larger than those of the motions from the interface events. The discrepancy of the offshore and onshore GMPM was significant, and the peak ground accelerations (PGAs) and SAs of the offshore ground motions were apparently greater than those of onshore ground motions of the same magnitude and distance. The offshore GMPM established by the reference empirical approach contribute to studying the characteristics of offshore strong ground motions, and this approach can be applied to data-poor regions.

Quantitative strong motion simulations at three locations in downtown Mashiki during the 2016 Kumamoto Earthquake (Mw 7.0) based on the nonlinear ground response analyses with soil liquefaction

The mainshock of the 2016 Kumamoto Earthquake (Mw 7.0) caused extensive damage to buildings in downtown Mashiki, Kumamoto Prefecture, Japan. The heavy building damage in the area was associated with both strong ground motion and building response characteristics. Fortunately, there were two strong motion stations in the area and the observed records during the mainshock were distributed, showing peak ground velocities exceeding 100 cm/s on the surface. The level of shaking would be sufficient to make soft surface sediments nonlinear. To reproduce observed ground motions quantitatively, one-dimensional nonlinear effective-stress time-history analyses were conducted at three locations in downtown Mashiki. The input wave was employed as either the observed underground wave or simulated outcrop input motion based on the diffuse field theory. The main purpose of the study was twofold: to investigate the proper soil constitutive relationship and its nonlinear parameters based on the limited amount of in situ information, and to validate the method of input motion evaluation at the seismological bedrock level based on diffuse field theory. The nonlinear time history analyses using the on-site boring survey and the outcrop wave based on diffuse field theory showed that the waveform of the mainshock observed on the ground surface was explained with sufficient accuracy. In addition, the results of the effective stress analysis indicated that soil liquefaction might have occurred in the area with thick surface layers along the Akitsu River where the water table was considered to be quite shallow.Graphical

A Novel Pulse-Based Estimation of Response Spectra for Strong Ground Motions

ABSTRACT A method is proposed to quantitatively capture the unique characteristics of strong ground motions using idealized pulses. The pulse motions described here use limited parameters (PGA or PGV and duration of pulse) in contrast to the methodologies involving several parameters and assumptions. This simple method also provides an advantage to specify hazard in regions where a few recorded ground motions are available; ballpark values of pulse parameters can be used to arrive at the response spectra required in the seismic design. The physics of ground shaking is captured here mathematically using idealized pulses only, without any “random shaking.”

Characteristics of Strong Ground Motions from Four M S ≥ 5.0 Earthquakes in the 2021 Yangbi, Southwest China, Seismic Sequence

ABSTRACT A seismic sequence has struck the Yangbi county, west part of Yunnan Province in southwest China since May 18, 2021 . This region experienced the strongest ground shakings on the night of 21 May with the successive occurrence of four earthquakes with M S ≥5.0 in a short time and more small earthquakes. Large numbers of strong-motion recordings obtained in the four earthquakes with M S ≥5.0 (i.e. the M S 5.6 foreshock, the M S 6.4 mainshock, the M S 5.0 and M S 5.2 aftershocks) were analyzed in detail to characterize the source effects, distance decay, etc. The velocity pulse-like waveform at near-source station 53YBX and the significant asymmetry of distance decay along the SSE-NNW direction (i.e. much slower toward the SSE) in the M S 6.4 mainshock seem to hint the occurrence of the asymmetrical source rupture. The source rupture directivity for the four events were investigated by fitting the azimuth-dependent residuals of the PGAs. The M S 6.4 mainshock is characterized by the significantly asymmetrical bilateral rupture propagation, predominantly in the SSE direction with a rupture velocity of about 2.24 km/s. The PGA and PSAs from the four earthquakes were further compared with the predicted medians of the ASK14 and CY14 prediction models for global shallow crustal earthquakes. The negative inter-events residuals reflect the weaker source contributions of the Yangbi events to ground motions. The source contributions to short-period ground motions approximately show the dependence on earthquake type, that is, M S 5.6 foreshock > M S 6.4 mainshock > M S 5.2 aftershock, consistent with the dependence of stress drop on earthquake type. We further noted that the inter-events values for the M S 5.0 aftershock are far below those for the M S 5.2 aftershock. This may be attributed to the differences in the spatial and temporal distance to the mainshock, that is, weak source contributions from the close aftershocks to the mainshock. The values of adjustment coefficient Δc 3 are almost positive, indicating the weaker anelastic attenuations in the study region. Finally, we also found that the distance scaling of significant duration can be well described by both empirical models (AS16 model for predicting significant duration and the BT14 model for empirically illustrating the ground-motion path duration).

Strong ground motion data of the 2015 Gorkha Nepal earthquake sequence in the Kathmandu Valley

Strong-motion records of earthquakes are used not only to evaluate the source rupture process, seismic wave propagation and strong ground motion characteristics, but also to provide valuable data for earthquake disaster mitigation. The Kathmandu Valley, Nepal, which is characterised by having soft sediments that have been deposited in an earthquake-prone zone, has experienced numerous earthquakes. We have operated four strong-motion stations in the Kathmandu Valley since 2011. These stations recorded the 2015 magnitude 7.8 Gorkha Nepal earthquake that occurred in the Himalayan continental collision zone. For several months after the mainshock, we deployed four additional temporary stations. Here, we describe the seismic data for 18 earthquakes over magnitude 5.0 collected by this array, including the 2015 magnitude 7.3 Dolakha earthquake of maximum aftershock and three large aftershocks of magnitude 6-class. These data are essential for validating the sedimentary structure of the basin and for evaluating the hazard and risk of future earthquakes in the Kathmandu Valley.

Characteristics of Strong Ground Motions in the 30 October 2020, MW6.9 Aegean Sea Earthquake

The eastern parts of the Aegean Sea were struck by a destructive MW 6.9 earthquake on 30 October 2020 at 11:51:27 UTC. The earthquake ruptured an East-West trending normal fault in the Aegean Sea between the northern coast of Samos Island and the southern coast of İzmir and also triggered a medium level tsunami and thousands of aftershocks across the region. 119 fatalities, 1,051 injuries, and many collapsed buildings were reported due to the earthquake in the affected region. The most catastrophic consequences of the earthquake were registered in the Bayraklı and Bornova districts, which are built on a deep alluvial Basin approximately 60–70 km away from the epicentre of the mainshock. This paper explains the damage with an extensive dataset of ground motion records of the mainshock and aftershocks, which are provided by both Greek and Turkish networks. A set of ground motion parameters such as peak ordinates, spectral quantities, intensity measures and duration parameters are calculated and analysed. The closest softer soil station in Samos Island produces the highest peak ground acceleration and velocity. The ground motion models employed commonly for the region overestimate the observed data beyond 60–70 km of Joyner-Boore distance except for the recently published local ground motion model, which utilises local earthquakes in the derivation of the model. Contrary to expectations, stiff soil recordings exhibit considerable spectral accelerations in the long period region, similar to those in soft soils. The calculated ground motion parameters are correlated with the results of the hybrid reconnaissance mission, organized by the Earthquake Engineering Field Investigation Team (EEFIT). Although the peak values and regarded intensity measures clearly highlight the variability in soil conditions in the most damaged area (Bayraklı and Bornova), velocity-based ground motion parameters seem to be the more responsive damage indicators. The spectral shapes of the normalised response spectra in the İzmir Basin are not compatible with the 2018 Turkish seismic code spectrum whereas their response spectra are below the 475-years return period design spectra provided in outdated and current Turkish seismic codes.

Strong Motions on Land and Ocean Bottom: Comparison of Horizontal PGA, PGV, and 5% Damped Acceleration Response Spectra in Northeast Japan and the Japan Trench Area

ABSTRACT A large-scale permanent ocean-bottom seismograph network, named S-net, has been established in the Japan Trench area and consists of 150 observatories equipped with seismometers and tsunamimeters. Most stations at water depths <1500 m were buried to a depth of about 1 m while they were sited freely on the seafloors at greater water depths. To understand the characteristics of strong ground motions on the offshore area, we compared the horizontal vector peak ground accelerations (PGA), peak ground velocities (PGVs), and acceleration response spectra (ARS) between the land and S-net sites for nine earthquakes (5.3≤Mw≤7.1) using ground-motion prediction equations developed for Japan. We found that the observed values of PGAs and short-period (<0.5 s) ARS were generally similar between the land and S-net sites, whereas the PGVs and ARS for the periods longer than 0.5 s were apparently larger at the S-net sites. These results based on data covering a wide area on the seafloors were generally similar to the previous results based on limited ocean-bottom stations. However, analysis of the residuals, within the source-to-site distance of 200 km, revealed that the residual values were smaller in the shallow water region compared to those toward the Japan Trench, which is characterized by proximity to high Qs in the Pacific plate, the presence of thick unconsolidated sediments on the upper crust, and increasing heights of water columns. The difference of station settings in the shallow and deep water regions may also have contributed to the biased distribution of residuals at the short periods. Quantifications of these results are expected to contribute to the predictions of ground motions for earthquake early warning and seismic demand analysis of offshore facilities and await further analysis of a larger data set.

Questionnaire surveys on damages at high-rise buildings and synthesized near-fault long-period strong ground motions of the 2018 Hualien, Taiwan, earthquake

Long-period pulse-like strong ground motions were recorded near the Milun fault and caused serious building damages in the Hualien City during the main shock of the 2018 Hualien, Taiwan, earthquake. In this paper, questionnaire survey on feeling of shaking, indoor damages, structural, and nonstructural damages to high-rise reinforced concrete residential buildings were analyzed by three building groups according to the positions to the Milun fault and different site conditions. Relationships between the results of questionnaire survey on building damages and characteristics of strong ground motions were studied. Furthermore, a characterized seismic source model was proposed to elucidate the generation mechanism of near-fault long-period strong ground motions. In this model, a shallow strong motion generation area (SMGA7) in the south part of Milun fault with rise-time of 2.6 s contributed to the long-period pulse-like strong ground motions. Besides, a deep SMGA (SMGA8) under the SMGA7 with rise-time of 1.2 s also contributed to the strong ground motions. Using this model, strong ground motions at the sites of buildings for questionnaire survey were synthesized. Because of the directivity effects, amplitudes of ground motions were increased from north to south along the Milun fault, which can explain the serious building damages at the buildings located at the southwest to the Milun fault. The reasons of building damages were also examined from the aspect of predominant periods of ground sites and fundamental periods of buildings, which were extracted from microtremor measurement. Damages at the buildings located on the central part of the hanging wall with relatively good site condition were the lightest for almost all the surveyed items. Pulses with period in the range of 1 s–2 s which were generated by the SMGA8 and amplified by the near surface layers are considered to be responsible for building damages.

Predicting Near-Field Strong Ground Motion of the Huaxian Ms8.5 Earthquake Based on Uncertainty Factors of Asperities

The Weihe Plain is at high risk of disastrous earthquakes, such as the Huaxian Ms8.5 earthquake, which caused enormous casualties and economic losses. Therefore, reproducing the strong ground motion characteristics of the Huaxian earthquake is important for seismic design and disaster mitigation. The empirical Green’s function method is used to predict the ground motion characteristics of the Huaxian Ms8.5 earthquake by considering the uncertainty factors of asperities, considering the limited observations in the Weihe Plain and the inaccessibility of the Earth’s interior. The uncertainty asperity factors can be studied by the logic tree method, and source models considering these factors are constructed here. The uncertainty factors include the seismic moment M0, number of subfaults N, stress drop of an asperity Δσ, and asperity area Sa. The asperity area is assigned values of 19%, 22%, and 25% of the fault rupture area; the M0 values of the corresponding asperities account for 40%, 44%, and 48% of the entire M0; and there are two to four asperities. The permutations are combined into multiple-asperity source models. The two-asperity source models reflect the Huaxian earthquake characteristics better than the three- or four-asperity models. The asperity area accounts for approximately 22–25% of the fault rupture area, while the M0 of the corresponding asperities accounts for 44% and 48% of the entire M0. The long-axis direction of the ground motion distribution is the same as that of the mountains southeast of the Weihe Plain. The azimuth angle of the elliptical long axis is approximately 40–60° northeast. The greater the magnitude is, the more complex the number, location, and area of the asperities. This research extends the application of the empirical Green’s function method and can numerically simulate seismic intensity characteristics in areas with destructive earthquakes but few seismic records.

Strong Ground Motion Simulation for Forecasting the Probable Seismic Impacts in the Territory of the Republic of North Ossetia–Alania

Abstract—The models based on the empirical data are proposed for probabilistic forecasting the characteristics of strong ground motions (SGM) from the earthquakes, potentially dangerous for the territory of the Republic of North Ossetia–Alania. We consider the models of SGM characteristics that are most important in the engineering practice (macroseismic intensities of ground shaking, peak ground accelerations, periods, durations, spectra, and strong-motion accelerograms) in the vicinity of the sources of earthquakes of different magnitudes and at different distances from the sources in application to the seismogeological conditions of the study region. The models are developed using both the conventional statistical analysis of a large amount of data on instrumental recording and macroseismic description of the strong and perceivable earthquakes in the Caucasus and other seismically active regions of the world and a new method for reconstructing the spectra of the strong earthquakes from their macroseismic field. The cross-comparison of the estimates obtained based on the proposed models with each other and with the estimates obtained by the other authors has shown that they are fairly realistic and reliable.

Seismic risk analysis of concrete moment-resisting frames against near-fault earthquakes

Characteristics of earthquake strong ground motions play an important role in the calculation of seismic-induced risk imposed on the structures. Distinguished features exist in movements recorded near seismic sources, as a result of a substantial amount of energy in a short period of record arrival time. In this article, seismic risk analysis of concrete moment-resisting frames due to near-fault strong ground motion is calculated and compared with that of caused by far-field strong ground motions. To achieve this goal, three moment-resisting frames with 4, 6, and 10 stories were designed based on international seismic design code. These frames are modeled applying modified Ibarra–Krawinkler moment–rotation nonlinear model in which strength and stiffness deterioration are involved. Seismic risk analysis of the frames is implemented using the Pacific Earthquake Engineering Research Center approach. Through this approach, probabilistic seismic hazard, probabilistic structural demand, probabilistic structural damage, and probabilistic loss curves are combined. Mean annual frequency of exceedance of seismic-induced losses presents probabilistic seismic risk of the sampled frames. According to the achieved results, the four-story frame (representative of low-rise frames) is more prone to be affected by near-fault strong ground motions in view of calculated seismic-induced risks.

Probabilistic seismic hazard analysis and construction of design spectra for Pokhara valley, Nepal

Pokhara is one of the most naturally beautiful cities in the world with a unique geological setting. This largest metropolitan city in Nepal, having experienced a number of destructive earthquakes over the past centuries, is under intense pressure from rapid urbanization and population growth. The latest Gorkha earthquake (epicenter 70 km from Pokhara) occurred on 25th April 2015 of Magnitude 7.8 (Mw) killed nearly 9000 people and injured more than 22,000 people in Nepal. It was the worst natural disaster to strike Nepal since the 1934 great Nepal-Bihar earthquake (Mw = 8.0). With these recent seismic events flourishing new data, the heightened possibilities of a larger earthquake in this region have come forth. To this end, the probabilistic techniques were used to predict the expected future strong ground motion characteristics in the study area. For this, a probabilistic seismic hazard assessment (PSHA) is done by considering all the possible seismic events of historical earthquakes by dividing the whole area of interest into seven areal source zones. Based on the available data from each source zone, the frequency–magnitude relationship has been established after the elimination of dependent events followed by the completeness check of the data. Peak ground acceleration and spectral acceleration for 2% and 10% probabilities of exceedance in 50 years are estimated for predefined bedrock conditions with rock and soil sites, respectively. The resulting uniform hazard spectra (UHS) represent the approximate seismic loading on the structures. The estimated ground motion parameters in the present study have higher values compared with the values suggested in the earthquake-resistant design codes in standard practice. The study also proposed the design response spectra for the study area, which is much more defensible in engineering decision-making for reducing seismic risk.

The Neo-Deterministic Seismic Hazard map (NDSHA) of Sumatra compared with official 2010 and 2017 derived from PSHA method

Typical seismic hazard problem lies on determination of ground motion characteristics associated with future earthquakes. Strong ground motion characteristics such as Peak Ground Acceleration (PGA) is important information for engineers in order to provide earthquake resistant building. The Indonesian government has provided update of maps of PGA by released a series official PSHA (Probabilistic Seismic Hazard Assessment) maps in 1978, 2002, 2010 and 2017. On the other hand, the NDSHA (Neo-Deterministic Seismic Hazard Assessment) method has been developed and successfully applied to Sumatra. Because of the availability of numerical PGA data for the official PSHA 2010 and 2017, this paper discusses the comparison of PGA between derived from NDSHA and that of official PSHA updated in 2010 and 2017. The spatial resolution of the PGA digital map of PSHA is 0.01 degree and NDSHA is 0.1 degree. Due to the different resolution, a program and a script are developed to incorporate PSHA data into the NDSHA data points by performing interpolation procedure. The comparison results show the PGA of PSHA 2017 is significantly greater than PGA PSHA 2010. However, the PGA values of the 2017 PSHA map are lower than that of PSHA 2010 such as along the Sumatran fault in Central and South Sumatra. The PGA values estimated by using standard NDSHA with 10 Hz cut-off is higher than those of the computed PGA from PSHA at PE (Probability of Exceeding) of 2% in 50 year for official map released in 2010 and 2017. For comparison with PE of 2% in 50 year, the near field NDSHA gives the PGA value greater than that of the PSHA; and for the far field sources. This means the NDSHA calculation for Sumatra gives reasonable results based on the adopted magnitude distance threshold. This is due to the fact that the standard NDSHA is based on the realistic physical simulation of the seismic wave propagation. The comparison between the PGA computed based on the proposed enhanced version of NDSHA and PSHA shows that the updated version gives the same values at near field and lower values at the far sites; whereas the standard one gives a higher value in NDSHA, which in turn gives a higher PGA value for the near and far field sources.

Analysis of strong ground motion characteristics recorded on reclaimed soil site

This paper discusses the difference between the strong ground motion of reclaimed soil sites and those of free-field ground motion. We determine under what conditions the influence of reclaimed soil can be ignored, and the ground motion on the reclaimed soil site can be regarded as a free field. Finite element models of reclaimed soil were constructed by analyzing the actual situation of strong ground motion observation on reclaim soil sites. Using a “lumped mass explicit dynamic finite element” method, the effects of shear wave velocity and thickness of reclaimed soil on free-field ground motion are analyzed. Replacing thicker reclaimed soil with remolded soil is proposed to reduce the impact of reclaimed soil sites on the ground motion of free field sites, the effects of which are analyzed by numerical simulation. Results show that the ground motion peak and the response spectra of the reclaimed soil site are significantly different from those of the free field site. With increasing reclaimed soil thickness, the influence is more noticeable. The impact of reclaimed soil on the free-field site can be reduced with reclaimed soil being replaced by remolding soil. The conclusions provide a theoretical basis for the rational use of strong ground motion records on the reclaimed soil site and the construction of strong motion stations.

Earthquake Cycle Modelling of Multi-segmented Faults: Dynamic Rupture and Ground Motion Simulation of the 1992 Mw 7.3 Landers Earthquake

We perform earthquake cycle simulations with the goal of studying the characteristics of source scaling relations and strong ground motions in multi-segmented fault ruptures. The 1992 Mw 7.3 Landers earthquake is chosen as a target earthquake to validate our methodology. The model includes the fault geometry for the three-segmented Landers rupture from the SCEC community fault model, extended at both ends to a total length of 200 km, and limited to a depth to 15 km. We assume the faults are governed by rate-and-state (RS) friction, with a heterogeneous, correlated spatial distribution of characteristic weakening distance Dc. Multiple earthquake cycles on this non-planar fault system are modeled with a quasi-dynamic solver based on the boundary element method, substantially accelerated by implementing a hierarchical-matrix method. The resulting seismic ruptures are recomputed using a fully-dynamic solver based on the spectral element method, with the same RS friction law. The simulated earthquakes nucleate on different sections of the fault, and include events similar to the Mw 7.3 Landers earthquake. We obtain slip velocity functions, rupture times and magnitudes that can be compared to seismological observations. The simulated ground motions are validated by comparison of simulated and recorded response spectra.

Strong Ground Motion Characteristics from 2016 Central Italy Earthquake Sequence

The Central Italy earthquake sequence has, to date, generated three mainshocks: M6.1 24 August, M5.9 26 October, and M6.5 30 October 2016. These events, along with aftershocks, were well recorded by Italian networks, and are among the normal fault earthquakes with the highest number of recordings globally. We process records for six events using procedures developed during the latest Next Generation Attenuation (NGA-West2) project, coordinated by the Pacific Earthquake Engineering Research Center (PEER). Many recording sites lacked VS30assignments, which we provide using measured shear wave velocity profiles where available and a local geology proxy otherwise. Stations at close distance, including near the hanging wall, exhibit fling step in some cases but no obvious rupture directivity. The data exhibit fast anelastic attenuation at large distances (>100 km), as predicted by recent Italy-adjusted global models, but not by Italy-specific models. We partition residuals from Italy-adjusted global models, finding negative event terms at short periods (weaker than average shaking). We apply Kriging of within-event peak acceleration and velocity residuals using a global semi-variogram model to estimate the spatial distribution of peak accelerations and velocities, which are generally most intense southwest of Mt. Vettore.

Amplification of thickness and topography of loess deposit on seismic ground motion and its seismic design methods

The Loess Plateau in China is a region with the biggest thickness and most complicated topography of loess deposit in the world, where is affected by strong earthquakes frequently. The seismic amplification effects were discovered in the Plateau during the Wenchuan Ms8.0 earthquake and some other strong events. The field investigations, observations, and analyses indicated that large number of casualties and tremendous economic losses were caused not only by collapse and damage of houses with poor seismic performance, landslides, liquefaction and seismic subsidence, but also amplification effects of thickness and topography of loess deposit on seismic ground motion. In this paper, the characteristics of strong ground motion recorded in the region were analyzed; shaking table tests were performed and numerical analysis was carried out on amplification of thickness and slope of loess deposit on seismic ground motion. Moreover, we also developed site amplification factors of ground motion for seismic design of engineering projects on loess sites. The results showed that the amplification effects are more predominant with increase of thickness and slope of loess deposit. The ground motion may be amplified in seismic intensity by 1–2°, PGA by 1.1–2.2 times, and predominant period by 1.1–1.6 times respectively.