Abstract: The Dominican Republic (DR) comprises the eastern two-thirds of the island of Hispaniola, which is located on the Caribbean-North American plate boundary. Geological studies have led to a description of the shallow structure and stratigraphy of the island but little is known about the lower crust and mantle due to a dearth of broadband seismic data. Since August 2013 a seismic network consisting of 20 broadband, three-component seismic stations has been deployed in the DR. Here we report on a receiver function study of crustal thickness and bulk composition using teleseismic P-wave data. We compute teleseismic receiver functions using an iterative time domain deconvolution technique and determine crustal properties via H-κ stacking. Three distinct, fault-bounded crustal domains, defined by characteristic Moho depths and bulk crustal Vp/Vs, are found in the DR. In the northern domain, the Moho has an average depth of ~32 km with Vp/Vs ratio 1.84 ± 0.1. Moho depths in the southern domain average ~ 33 km and Vp/Vs averages 1.68 ± 0.1. Thicker crust is found beneath the Cordillera Central, in the island’s center, where Moho depths average ~ 39 km and Vp/Vs is ~1.72 ± 0.1, while the crust at coastal areas of Dominican Republic has Moho depths of ~ 29 km and Vp/Vs of 1.77 ± 0.1. An E-W transect across the island’s center and four N-S transects were produced to show variations of crustal thickness and bulk Vp/Vs ratios. We interpret the southern domain to be a terrane accreted from the Caribbean Large Igneous Province. The thicker crust and average Vp/Vs ratio in the island’s center likely indicates an igneous root of the Cordillera Central, which includes Pico Duarte, the highest peak in the Caribbean.
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Abstract: The main purpose of this study is to develop ground motion prediction equations (GMPEs) for the Gulf Coast region of the United States using a hybrid empirical method (HEM). This project contributes toward development of a new set of GMPEs for the Gulf Coast region, which will be consistent with the available recordings. This research supplement recent GMPEs developed by the Pacific Earthquake Engineering Research Center (PEER) Next Generation Attenuation (NGA-East) GMPEs for the Central and Eastern North America (CENA) regions. Recently, a number of GMPEs for CENA are developed as part of NGA-East project conducted by the PEER. However, in majority of them, ground motions recorded in the Gulf Coast region were excluded due to considerably different attenuation attributes in this region (EPRI, 1993). The Gulf Coast region exhibits significantly different ground-motion attenuation because of the thick sediments in the region (Dreiling et al. 2014). The purpose of this study is to develop specific GMPEs for use in the Gulf Coast region using the HEM. Because the strong motion data set is sparse in the Gulf Coast region, the hybrid empirical method represents an appropriate and robust approach which has been generally accepted to develop GMPEs.
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Abstract: The Nevada Bureau of Mines and Geology and the Nevada Seismological Laboratory convened the Working Group on Nevada Seismic Hazards in February 2018. The purpose of the workshop was to review ongoing earthquake hazard research in Nevada, provide insight and advice regarding technical issues related to earthquake hazards, and to identify priorities for future research that will benefit the National Seismic Hazard Map (NSHM). The workshop will occur after the abstract deadline for this meeting, so outcomes were not known when this abstract was prepared. Our presentation will summarize the outcomes of the workshop as they pertain to future updates of the NSHM. Specifically, we will present research priorities for paleoseismic, seismologic, geophysical, and geodetic studies determined to be important for improving the NSHM in the Reno/Carson/Lake Tahoe and Las Vegas urban areas. Building on the outcomes of the workshop, it is anticipated that future collaborative research between the USGS, State government, and academia will contribute valuable information to the NSHM.
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Abstract: The September 7 Tehuantepec, Mexico (M=8.2) and the September 19 Morelos-Puebla, Mexico (M=7.1) earthquakes ruptured with extensional faulting within the Cocos Plate at ~70-km and ~50-km depth, respectively, as it subducts beneath the continental North American Plate. Both earthquakes caused significant damage and loss of life. These events were followed by a M=6.1 extensional earthquake at only ~10-km depth in Oaxaca on September 23, 2017. Many questions remain about these earthquakes, including: Did the Cocos Plate earthquakes load the upper plate, and could they possibly trigger an equal or larger earthquake on the plate interface? Are these the result of plate bending? Do the aftershocks migrate to the locked zone in the subduction zone? Why did the intermediate depth earthquakes create so much damage? Are these earthquakes linked by dynamic stresses? Is it possible that a potential slow-slip event triggered both events? To address some of these questions, we deployed 10 broadband seismometers near the epicenter of the Tehuantepec, Mexico earthquake and 51 UTEP-owned nodes (5-Hz, 3-component geophones) to record aftershocks and augment temporary and permanent networks deployed by the Universidad Nacional Autónoma de México (UNAM). The 10 broadband instruments were in place in early Oct. 2017 and will be deployed for 6 months, while the nodes were deployed 25 days. Using data from our temporary network for the first several months of the deployment plus UNAM permanent stations from this same time window, we build an initial database of automated detections and locations of the aftershocks, using detection and association parameters optimized for local seismic networks. Our initial analysis will allow us to investigate fault geometries from the aftershock locations, and in the future, will allow for the analysis of stress release and orientation from the determination of fault plane solutions, plus site effects and characteristics in regions of extensive damage.
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Abstract: The Mw7.8 Pedernales earthquake is associated with the subduction of the Nazca Plate beneath the South American Plate. The mainshock caused many casualties and widespread damages across the Manabi province. The 150 km-long coseismic rupture area is found beneath the coastline, near 25 km depth. The rupture propagated southward and involved the successive rupture of two discrete asperities, with a maximum slip (~ 6 m) on the southern patch. The rupture area is consistent with the highly locked regions observed on interseismic coupling models, overlaps the 7.2 Mw rupture zone, and terminates near where the 1906 Mw 8.8 megathrust earthquake rupture zone ends. Two neighboring highly coupled patches remain locked: (A) southern to and updip of the coseismic rupture zone and (B) northern and downdip. In this study, we relocate the aftershocks and compare the seismicity distribution to the interseismic coupling and the rupture area. We use continuous seismic traces recorded on the permanent network partly installed in the frame of the collaboration between l’Institut de Recherche pour le Développement (IRD-France) and the Instituto Geofísico, Escuela Politécnica Nacional, Quito, Ecuador. Detections are conducted using Seiscomp in play-back mode. Arrival-times are manually picked. To improve earthquake location, we use the MAXI technique and a heterogeneous a priori P-wave velocity model that approximates the large velocity variations of the Ecuadorian subduction system. Aftershocks align along 3 to 4 main clusters that strike perpendicularly to the trench, and mostly updip of the co-seismic rupture. Aftershock seismicity develops indifferently over portions of plate interface that are known to be strongly locked or almost uncoupled. The seismicity pattern is similar to the one observed during a decade of observation during the interseismic period with swarms such as the Galera alignment, Jama and Cabo Pasado, and between Manta and Puerto Lopez.
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Abstract: The main purpose of this study is to develop a new Ground Motion Model (GMM) for the island of Hawaii using the hybrid empirical method (HEM). The HEM uses stochastically simulated Ground Motion Intensity Measures (GMIMs) in the host and target regions to develop adjustment factors that are applied to empirical GMIM predictions in the host region. The island of Hawaii, the target region in this study, has been the site of numerous large earthquakes. The crustal earthquakes in the island of Hawaii originate from volcanic activity and include both swarms of small-magnitude volcanic events and larger tectonic events. Considering western North America as the host region, we will use five NGA-WEST2 GMMs developed by the Pacific Earthquake Engineering Research center. For the required seismological parameters in western United States, we will use Zandieh et al. (2017) results in which a set of point-source inversions have been performed to match the median NGA-West2 GMPEs for moment magnitudes M of 3.0–8.0, rupture distances of 1–400 km, spectral periods of 0.01–10 sec, and NEHRP B/C boundary site conditions. For the island of Hawaii, we will use results of an ongoing study by Haji-Soltani and Pezeshk (2018) in which the geometrical spreading and quality factor functions are investigated for the island of Hawaii. The new GMM will be derived for the 5%-damped pseudo-acceleration response spectra for a reference rock site with VS30 = 760 m/s. A moment magnitude range of 4.0 to 8.0 and rupture distances of up to 400 km will be considered.
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