Shallow Crustal Earthquakes Research Articles

Selection and Modification of Ground Motion Prediction Equations in Different Tectonic Regions of Iran considering Declustered and Non-declustered Earthquake Catalogs

ABSTRACT Shallow crustal earthquakes (SCE) occur in different seismotectonic regions of the Iranian plateau. In this study, 10 ground motion prediction equations (GMPEs) developed based on local, regional, and global data from SCE are considered as candidates to test their explanatory power against Iranian strong motion data. To show the applicability of candidate GMPEs in the plateau as a united region and its different seismotectonic sub-regions, a dataset including 3045 records from 678 seismic events (both mainshocks and aftershocks) is used for statistical analyses. Moreover, using 1662 records from 245 mainshocks, we tried to find more appropriate GMPEs against mainshock ground motions through statistical tests. This work also concentrates on differences in ground motions from mainshock and aftershock earthquakes using the Iranian database. The statistical analyses including LH (Likelihood), LLH (Log-Likelihood) and EDR (Euclidean distance-based ranking) are also performed on GMPEs modified by a local anelastic term. According to the LH and LLH analyses results, local and regional models have better performances for PGA and spectral accelerations (SA) at different periods ranging from 0.05 to 3 sec. However, according to the EDR test, it can be said that some global GMPEs also show acceptable performance for predicting the Iranian ground motions. Also, the adjustment factors added to the GMPEs can considerably improve their explanatory performance.

Near-source magnitude scaling of spectral accelerations: analysis and update of Kotha et al. (2020) model

Ground-motion models (GMMs) are often used to predict the random distribution of Spectral accelerations ( $$\mathrm{SAs}$$ ) at a site due to a nearby earthquake. In probabilistic seismic hazard and risk assessment, large earthquakes occurring close to a site are considered as critical scenarios. GMMs are expected to predict realistic $$\mathrm{SAs}$$ with low within-model uncertainty ( $${\upsigma }_{\upmu }$$ ) for such rare scenarios. However, the datasets used to regress GMMs are usually deficient of data from critical scenarios. The (Kotha et al., A Regionally Adaptable Ground-Motion Model for Shallow Crustal Earthquakes in Europe Bulletin of Earthquake Engineering 18:4091–4125, 2020) GMM developed from the Engineering strong motion (ESM) dataset was found to predict decreasing short-period $$\mathrm{SAs}$$ with increasing $${M}_{W}\ge {\mathrm{M}}_{\mathrm{h}}=6.2$$ , and with large $${\upsigma }_{\upmu }$$ at near-source distances $$\le 30\mathrm{km}$$ . In this study, we updated the parametrisation of the GMM based on analyses of ESM and the Near source strong motion (NESS) datasets. With $${\mathrm{M}}_{\mathrm{h}}=5.7$$ , we could rectify the $${M}_{W}$$ scaling issue, while also reducing $${\upsigma }_{\upmu }$$ at $${M}_{W}\ge {\mathrm{M}}_{\mathrm{h}}$$ . We then evaluated the GMM against NESS data, and found that the $$\mathrm{SAs}$$ from a few large, thrust-faulting events in California, New Zealand, Japan, and Mexico are significantly higher than GMM median predictions. However, recordings from these events were mostly made on soft-soil geology, and contain anisotropic pulse-like effects. A more thorough non-ergodic treatment of NESS was not possible because most sites sampled unique events in very diverse tectonic environments. We provide an updated set of GMM coefficients, $${\upsigma }_{\upmu }$$ , and heteroscedastic variance models; while also cautioning against its application for $${M}_{W}\le 4$$ in low-moderate seismicity regions without evaluating the homogeneity of $${M}_{W}$$ estimates between pan-European ESM and regional datasets.

Stochastic Simulation of Strong Ground Motions From Two M > 5 Uttarakhand Earthquakes

Many studies based on the geodetic data and statistical analysis of seismicity have pointed out that sufficient amount of stress accumulated in the Himalayan plate boundary may host a big earthquake. Consequently, high seismic activities and infrastructural developments in the major cities around Himalayan regions are always of major concern. The ground motion parameter estimation plays a vital role in the near real time evaluation of potentially damaged areas and helps in mitigating the seismic hazard. Therefore, keeping in mind the importance of estimation of ground motion parameters, we targeted two moderate-size earthquakes that occurred recently within a gap of 10 months in Uttarakhand region with M > 5.0 on 06/02/2017 and 06/12/2017. The ground motions are simulated by adopting a stochastic modeling technique. The source is assumed as ω−2, a circular point source (Brune’s model). The average value of reported anelastic attenuation from various studies, the quality factor, Qs= 130.4*(f0.996), and stress drop values obtained through iterative procedure are considered for simulations. The stochastic spectra are generated between 0.1 and 10 Hz of frequency range. The site effect is also estimated by using the H/V method in the same frequency range. The synthetic spectra are compared with the observed Fourier amplitude spectra obtained from the recorded waveform data and converted back to the time histories. The stochastic time histories are compared with the observed waveforms and discussed in terms of amplitude (PGA). The simulated and observed response spectra at different structural periods are also discussed. The mismatch between the observed and simulated PGA values along with the GMPE existing for shallow crustal earthquakes is also discussed in the present work.

The Spatio-temporal Tectonic Condition and Microzonation Map of Malang Region after the 2021 M6.1 Malang Earthquake for Disaster Risk Mitigation

The M6.1 earthquake which hit Malang and its surroundings in 2021 resulted in fatalities and over 10,400 damaged houses. Several seismicity studies have been carried out for Malang region, but no specific studies have implied the M6.1 Malang earthquake yet. This study addresses such gap by investigating the Spatio-temporal b-value of Gutenberg-Richter Law and generating the microzonation maps of spectral acceleration by considering the effects of the M6.1 Malang earthquake. The earthquake data compiled from the national and international earthquake catalogs were homogenized into a moment magnitude scale. The b-value analysis was calculated using the Maximum Likelihood method and spatio-temporal mapping. Several ground motion prediction equations (GMPEs) were selected for subduction and shallow crustal earthquake sources to generate probabilistic seismic hazard analysis (PSHA). PSHA was conducted using the 2% probability of exceedance in 50 years. The results show that the b-value after the M6.1 Malang earthquake still tends to decrease, indicating a relatively-high stress level which accommodates the potential for large earthquakes in the future. The microzonation maps for Malang region show that the southern part of Malang has a higher spectral acceleration value than the others. Therefore, these findings can be considered in the future disaster mitigation plan.

A regionally adaptable ground-motion model for fourier amplitude spectra of shallow crustal earthquakes in Europe

Typical seismic ground-motion models predict the response spectral ordinates (GMM-SA), which are the damped responses of a suite of single-degree-of-freedom oscillators. Response spectra represent the response of an idealized structure to input ground-motion, but not the physics of the actual ground-motion. To complement the regionally adaptable GMM-SA of Kotha et al. (2020), we introduce a model capable of predicting Fourier amplitudes (GMM-FA); developed from the Engineering Strong Motion (ESM) dataset for pan-Europe. This GMM-FA reveals the very high variability of high frequency ground-motions, which are completely masked in a GMM-SA. By maintaining the development strategies of GMM-FA identical to that of the GMM-SA, we are able to evaluate the physical meaning of the spatial variability of anelastic attenuation and source characteristics. We find that a fully data-driven geospatial index, Activity Index (AIx), correlates well with the spatial variability of these physical effects. AIx is a fuzzy combination of seismicity and crustal parameters, and can be used to adapt the attenuation and source non-ergodicity of the GMM-FA to regions and tectonic localities sparsely sampled in ESM. While AIx, and a few other parameters we touch upon, may help understand the spatial variability of high frequency attenuation and source effects, the high frequency site-response variability—dominating the overall aleatory variance—is yet unresolvable. With the rapid increase in quantity and quality of ground-motion datasets, our work demonstrates the need to upgrade regionalization techniques, site-characterisation, and a paradigm shift towards Fourier ground-motion models to complement the traditional response spectra prediction models.

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.

Integrating Effects of Source-Dependent Factors on Sediment-Depth Scaling of Additional Site Amplification to Ground-Motion Prediction Equation

ABSTRACT It is crucial to include additional site amplification effects resulting from the thick sediment on ground motions in the reliable assessment for seismic hazard in sedimentary basins. Ground-motion residual analysis with respect to ground-motion prediction equation is performed to evaluate additional site amplifications at over 200 K-NET stations within and around Kanto basin. We first investigate the potential effects on additional site amplifications resulted from the sediment depth and several source-dependent factors. Results reveal that source-to-site distance, focal depth, and source azimuth all have nonnegligible effects on additional site amplifications, especially the focal depth. Thick sedimentary sites amplify long-period ground motions from distant earthquakes more strongly than those from local earthquakes. Ground motions from shallow crustal earthquakes generally experience much stronger amplifications than those from those deep subduction earthquakes, much more predominant for long-period ground motions (>1.0 s) at thick sedimentary sites. Meanwhile, we develop the empirical model after integrating contributions from sediment depth, source-to-site distance, and focal depth for predicting additional site amplification effects. Considering the typical case of the distant shallow crustal earthquakes, additional site amplifications at thick sedimentary sites within Kanto basin generally show an increasing trend with the oscillation period increased, whereas they are generally characterized by a decreasing trend at shallow sedimentary sites outside the basin. The mean additional site amplification is up to about 2.0 within Kanto basin, whereas 0.5–0.65 outside Kanto basin, for ground motions at oscillation periods of 2.0–5.0 s. Mean amplifications within Kanto basin are about 3.5 times larger than those outside the basin for long-period ground motions at 2.0–5.0 s. Sites northeast to Kanto basin show the largest amplifications up to about 3.0 at periods of 0.15 and 5.0 s, which may be resulted from the basin edge effects.

Unexpected Shallow Earthquake of August 1st, 2020 in the North of Indramayu, West Java, Indonesia

During the last one hundred years, there are no shallow seismicity in the north of Java. This area is dominated by intermediate and deep focus earthquakes due to the subducted Indo-Australian slab. An earthquake with magnitude ML 4.5 struck Indramayu, north of West Java on August 1, 2020. According to the Agency for Meteorology, Climatology, and Geophysics (BMKG), the earthquake was felt III MMI scale in Indramayu and its vicinity. We used waveform data from BMKG seismic station in West Java, then we picked P-and S-waves arrival times from each station and hypocenter location was determined by Geiger method. We have detected Pn before Pg phase on four BMKG seismic stations, indicating a shallow crustal earthquake. Our inversion show that the earthquake occurred in 6.1805° S, 108.2612° E with 5 km focus depth at 16:24:38 GMT+7. Our focal mechanism solution was determined by using moment tensor inversion shows a strike-slip faulting, which corresponds to the active fault in the north of Indramayu.

An empirical model for the vertical‐to‐horizontal spectral ratios for Italy

AbstractThis work presents a novel empirical Ground Motion prediction Model (GMM) for vertical‐to‐horizontal (VH) response spectral amplitudes up to 10 s, peak ground acceleration and velocity for shallow crustal earthquakes in Italy. Being calibrated on the most up‐to‐date strong motion dataset for Italian crustal earthquakes (ITA18), the model is consistent with the ITA18 GMM for the horizontal ground motion. This property makes the model useful in probabilistic seismic hazard assessment for Italy to derive compatible vertical and horizontal response spectra. To account for the increase of VH ratios in the proximity of the seismic source, an adjustment term is introduced to improve the prediction capability of the model in near‐source conditions, relying on the worldwide NEar‐Source Strong motion dataset (NESS). The proposed model uses a simple functional form restricted to a limited number of predictor variables, namely, magnitude, source‐to‐site distance, focal mechanism, and site effects, and the variability associated with both VH and V models is provided.

Displacement Hazard Analysis of Earth Structures Affected by Subduction Zone and Shallow Crustal Earthquakes

AbstractCommon practice for evaluating the seismic performance of earth dams uses design ground motions selected to be consistent with a target design response spectrum, which are subsequently used...

A Ground-Motion Prediction Equation for the Western and the Southwestern Parts of China Based on Local Strong-Motion Records and an Overseas Reference Model for the Vertical Component

ABSTRACT A ground-motion prediction equation for the vertical ground motions from the western and the southwestern parts of China (referred to as SWC) is presented in this study. Based on the Xing and Zhao (2021) study, the Zhao et al. (2017) model (referred to as ZHAO2017) for the shallow crustal earthquakes in Japan was used as the reference model. We used a bilinear magnitude-scaling function hinged at a moment magnitude (Mw) of 7.1. The magnitude-scaling rate for events with Mw>7.1 was determined by records from the SWC dataset and the large events in the Pacific Earthquake Engineering Research Center Next Generation Attenuation-West2 dataset. Site classes (SCs) were used as the site response proxy. All other parameters were derived from the SWC dataset only. The magnitude-scaling rates for events with Mw≤7.1 in this study are larger than in the ZHAO2017 model at most periods. The absolute values of the geometric attenuation rates are larger, and the absolute values of the anelastic attenuation rates are smaller than in the ZHAO2017 model. The between-event standard deviations are smaller than in the ZHAO2017 model at short periods, and the within-event standard deviations are larger than in the ZHAO2017 model at all periods. The differences in the between-site standard deviations vary significantly from one SC to another. We also find that the between-event and within-event residuals are almost independent of magnitude and source distance. The response spectrum attenuates less rapidly than in the ZHAO2017 model at distances less than 30 km.

Simulation of near-fault ground motions for randomized directivity parameters

The Dabaghi and Der Kiureghian stochastic near-fault ground motion model requires information about the source, site, and source-to-site geometry, including directivity parameters. Directivity parameters entail often unavailable knowledge of the rupture geometry and hypocenter location. This article presents methods to randomize the directivity parameters required to simulate near-fault ground motions. A first procedure is proposed where only the contributing fault, earthquake magnitude, and site location are known. Possible rupture directivity conditions are accounted for by randomizing the rupture geometry and hypocenter location. For this purpose, new predictive models of the rupture geometry parameters are developed for shallow crustal earthquakes with magnitudes between 5.2 and 7.9. To allow validation of synthetic motions with NGA-West2 models, a second procedure randomizes the rupture geometry and both hypocenter and site locations. Results show a general agreement between the two methods.

Spectral damping scaling factors for horizontal components of ground motions from subduction earthquakes using NGA-Subduction data

This article develops global models of damping scaling factors (DSFs) for subduction zone earthquakes that are functions of the damping ratio, spectral period, earthquake magnitude, and distance. The Next Generation Attenuation for subduction earthquakes (NGA-Sub) project has developed the largest uniformly processed database of recorded ground motions to date from seven subduction regions: Alaska, Cascadia, Central America and Mexico, South America, Japan, Taiwan, and New Zealand. NGA-Sub used this database to develop new ground motion models (GMMs) at a reference 5% damping ratio. We worked with the NGA-Sub project team to develop an extended database that includes pseudo-spectral accelerations (PSA) for 11 damping ratios between 0.5% and 30%. We use this database to develop parametric models of DSF for both interface and intraslab subduction earthquakes that can be used to adjust any subduction GMM from a reference 5% damping ratio to other damping ratios. The DSF is strongly influenced by the response spectral shape and the duration of motion; therefore, in addition to the damping ratio, the median DSF model uses spectral period, magnitude, and distance as surrogate predictor variables to capture the effects of the spectral shape and the duration of motion. We also develop parametric models for the standard deviation of DSF. The models presented in this article are for the RotD50 horizontal component of PSA and are compared with the models for shallow crustal earthquakes in active tectonic regions. Some noticeable differences arise from the considerably longer duration of interface records for very large magnitude events and the enriched high-frequency content of intraslab records, compared with shallow crustal earthquakes. Regional differences are discussed by comparing the proposed global models with the data from each subduction region along with recommendations on the applicability of the models.

A Suite of Alternative Ground-Motion Models (GMMs) for Israel

ABSTRACTModels for estimating earthquake ground motions are a key component in seismic hazard analysis. In data-rich regions, these models are mostly empirical, relying on the ever-increasing ground-motion databases. However, in areas in which strong-motion data are scarce, other approaches for ground-motion estimates are sought, including, but not limited to, the use of simulations to replace empirical data. In Israel, despite a clear seismic hazard posed by the active plate boundary on its eastern border, the instrumental record is sparse and poor, leading to the use of global models for hazard estimation in the building code and all other engineering applications. In this study, we develop a suite of alternative ground-motion models for Israel, based on an empirical database from Israel as well as on four data-calibrated synthetic databases. Two host models are used to constrain model behavior, such that the epistemic uncertainty is captured and characterized. Despite the lack of empirical data at large magnitudes and short distances, constraints based on the host models or on the physical grounds provided by simulations ensure these models are appropriate for engineering applications. The models presented herein are cast in terms of the Fourier amplitude spectra, which is a linear, physical representation of ground motions. The models are suitable for shallow crustal earthquakes; they include an estimate of the median and the aleatory variability, and are applicable in the magnitude range of 3–8 and distance range of 1–300 km.

Earthquake-induced debris flows at Popocatépetl Volcano, Mexico

Abstract. The 2017 Mw 7.1 Puebla–Morelos intraslab earthquake (depth: 57 km) severely hit Popocatépetl Volcano, located ∼ 70 km north of the epicenter. The seismic shaking triggered shallow landslides on the volcanic edifice, mobilizing slope material saturated by the 3 d antecedent rainfall. We produced a landslide map based on a semi-automatic classification of a 50 cm resolution optical image acquired 2 months after the earthquake. We identified hundreds of soil slips and three large debris flows for a total affected area of 3.8 km2. Landslide distribution appears controlled by the joint effect of slope material properties and topographic amplification. In most cases, the sliding surfaces correspond with discontinuities between pumice-fall and massive ash-fall deposits from late Holocene eruptions. The largest landslides occurred on the slopes of aligned ENE–WSW-trending ravines, on opposite sides of the volcano, roughly parallel to the regional maximum horizontal stress and to volcano-tectonic structural features. This suggests transient reactivation of local faults and extensional fractures as one of the mechanisms that weakened the volcanic edifice and promoted the largest slope failures. The material involved in the larger landslides transformed into three large debris flows due to liquefaction. These debris flows mobilized a total volume of about 106 m3 of material also including large wood, were highly viscous, and propagated up to 7.7 km from the initiation areas. We reconstructed this mass wasting cascade by means of field evidence, samples from both landslide scarps and deposits, and analysis of remotely sensed and rainfall data. Although subduction-related earthquakes are known to produce a smaller number of landslides than shallow crustal earthquakes, the processes described here show how an unusual intraslab earthquake can produce an exceptional impact on an active volcano. This scenario, not related to the magmatic activity of the volcano, should be considered in multi-hazard risk assessment at Popocatépetl and other active volcanoes located along volcanic arcs.

Warming affects soil metabolome: The case study of Icelandic grasslands

The effect of warming is stronger in arctic and sub-arctic latitudes than in temperate and tropical zones. We studied soil metabolomes along two soil-warming gradients (0 to +15 °C). One temperature gradient has been present for at least 50 years and possibly even centuries (long-term treatment), while the second gradient was created after a shallow crustal earthquake in 2008 (short-term treatment). Soil metabolomes at the two sites responded differently to warming. At the short-term warmed site, warming of ≤+3 °C already shifted soil metabolomic profiles relative to the controls, whereas at the long-term warmed site the soil metabolome only shifted at temperatures ≥+5 °C. Saccharides and amino acids, primary metabolites involved in protective mechanisms against heat, were the main compounds accumulated at the highest soil warming levels. Some secondary metabolites associated with a broad spectrum of stressors, like phenolic acids and terpenes, were also up-regulated. Across the IPCC scenario's, most climate models predict a substantial rise in mean annual temperature of up to 8 °C in the Arctic region by the end of the 21st century. Our results suggest that temperature increases of ≥+5 °C would permanently alter soil metabolomic profile, whereas smaller temperature increases of (≤+3 °C) would affect soil metabolome profile transiently, not permanently.

Relations between MaxRotD50 and Some Horizontal Components of Ground-Motion Intensity Used in Practice

ABSTRACT The most commonly used intensity measure of ground motion in earthquake engineering is the 5% damped spectral ordinate, which varies in different directions. Several different measures have been proposed over the years to combine the intensity of the two horizontal recorded ground motions to derive ground-motion models as well as for design purposes. This study provides the relation to seven previously used measures of horizontal ground motion with respect to a recently proposed orientation-independent measure of horizontal ground-motion intensity referred to as MaxRotD50. This new measure of horizontal intensity is defined as the median value of the maximum spectral ordinate of two orthogonal directions computed for all possible nonredundant orientations. The relations are computed using 5065 pairs of horizontal ground motions taken from the database of ground motions recorded in shallow crustal earthquakes in active tectonic regions developed as part of the Pacific Earthquake Engineering Research Center’s Next Generation Attenuation-West2 project. Empirically derived period-dependent relations are presented for three quantities that permit transforming any of the seven other definitions of horizontal ground-motion intensity to MaxRotD50, namely, (1) geometric mean of the ratio of MaxRotD50 to any of the seven other measures of intensities, (2) standard deviation of the natural logarithm of the ratio of MaxRotD50 to any of the seven other measures of intensities, and (3) the correlation between the natural logarithm of the ratio of MaxRotD50 to the other measures of intensities and the natural logarithm of the other measure of intensity. In addition, the influence of site class at the recording station, earthquake magnitude, and distance to the horizontal projection of the rupture is examined on the geometric mean of the ratio of MaxRotD50 to the median intensity of all nonredundant orientations (i.e., RotD50), showing negligible influence of site class and only a relatively small influence of magnitude and distance.

Closure to “Procedure for Estimating Shear-Induced Seismic Slope Displacement for Shallow Crustal Earthquakes” by Jonathan D. Bray and Jorge Macedo

Closure to “Procedure for Estimating Shear-Induced Seismic Slope Displacement for Shallow Crustal Earthquakes” by Jonathan D. Bray and Jorge Macedo

Ground-Motion Intensity Measure Correlations on Interface and Intraslab Subduction Zone Earthquakes Using the NGA-Sub Database

ABSTRACTThe NGA-Sub (subduction zone earthquake) database developed by the Pacific Earthquake Engineering Research center is used to derive new correlation coefficients for a number of ground-motion intensity measure (IM) parameters from ground motions in subduction zone earthquakes, considering both interface and intraslab tectonic settings. The IMs include peak ground acceleration, pseudospectral accelerations with periods from 0.01 to 10 s, Arias intensity, cumulative absolute velocity, peak ground velocity, and significant duration. Comparisons of the estimated correlation coefficients for ground motions from the interface and intraslab tectonic settings generally show a good agreement. Our estimations are also in good agreement with correlation coefficients estimated in previous studies that used ground motions from shallow crustal earthquakes, supporting the concept that any variation in correlation coefficients comes from spectral shape (i.e., the distribution of peaks and troughs) rather than tectonic region. This study also explores the influence of parameters such as magnitude, distance, and site conditions on the estimated correlation coefficients. We did not find apparent trends of the correlation coefficients with respect to these parameters. Finally, we propose analytical models to estimate correlation coefficients between the IMs explored in this study, considering both subduction interface and intraslab tectonic settings.

A Seismic Intensity Survey of the 16 April 2016 Mw 7.8 Pedernales, Ecuador, Earthquake: A Comparison with Strong-Motion Data and Teleseismic Backprojection

AbstractWe conducted a seismic intensity survey in Ecuador, following the 16 April 2016 Mw 7.8 Pedernales earthquake, to document the level of damage caused by the earthquake. Our modified Mercalli intensities (MMIs) reach a maximum value of VIII along the coast, where single, two, and multistory masonry and concrete designed buildings partially or completely collapsed. The contours of our MMI maps are similar in shape to the contour maps of peak ground acceleration (PGA) and peak ground velocity (PGV). A comparison of our seismic intensities with the recorded PGA and PGV values reveals that our MMI values are lower than predicted by ground-motion intensity conversion equations that are based on shallow crustal earthquakes. The image of the earthquake rupture obtained using teleseismic backprojection at 0.5–2.0 Hz is coincident with the region of maximum MMI, PGA, and PGV values, Thus, rapid calculation of backprojection may be a useful tool for guiding the deployment of emergency response teams following large earthquakes. The most severe damage observed was, primarily, due to a combination of poorly constructed buildings and site conditions.