Abstract: At least nine small seismic events were detected and located around the North Korean nuclear test site following the 3 September 2017 underground nuclear test. The magnitude of these shocks range from 2.3 to 3.5. Based on their proximity to the 3 September 2017 UNT, these shocks may be considered as aftershocks of the UNT. We assess the best method to classify these small events based on spectral amplitude ratios of regional P and S wave from the shocks. None of these shocks are classified as explosion-like based on P/S spectral amplitude ratios. We examine additional possible small seismic events around the North Korean test site by using seismic data from stations in South Korea and northeastern China including IMS seismic arrays, GSN stations, and regional network stations. A linear discriminant function based on Mahalanobis methods applied to P/S spectral ratios does a better job of screening events, than does a simple average of such ratios.
Slidecast:
https://vimeo.com/278019415
Abstract: The Alaska Transportable Array (ATA) is a broadband seismic network made up of 280 new and existing stations that uniformly cover Alaska and north-west Canada. Over five field season from 2013-2017, 194 new stations were installed. In order to meet the performance requirements for the network, new power systems and telemetry systems were designed and produced on a large scale. The majority of ATA stations are installed in completely off grid locations with no access to an established electrical grid or telecommunications network. These off grid stations are fully autonomous and use solar panels and batteries for power and satellite modems to transmit data in real time. The stations also integrate additional instrument packages that include pressure sensors, infrasound sensors and weather stations. ATA stations use a dual battery chemistry power system made up of rechargeable lithium batteries and sealed lead acid batteries to minimize the system’s weight and maximize its energy storage. Savings in weight and volume significantly reduce the cost and complexity of the logistics needed to move the equipment from where it’s fabricated to where it operates. The autonomous ATA stations use high bandwidth satellite modems on the Inmarsat satellite network to transmit station data in near real time. The modems are configured to transmit station data in real time during the summer when incoming solar energy can be harvested with solar panels to keep the station batteries charged. In the winter months, the modems are operated in a lower power mode to maximize battery life yet still deliver data with less than 1 hour of latency. Additionally, autonomous ATA stations use very low power and low bandwidth Iridium modems to provide power system data as well as backup station state of health data in the event of a failure of the primary satellite modem. This state of health data helps operators troubleshoot the cause of outages and improves station service planning and success.
Slidecast:
https://vimeo.com/278026574
Abstract: The Southern California Earthquake Center (SCEC) has been collaborating with the National Hazard Engineering Research Infrastructure (NHERI) to deliver simulated ground motions through a new web tool on the NHERI cyberinfrastructure portal, DesignSafe-CI. The NHERI DesignSafe-CI offers opportunities for engineering research for multiple natural hazards and integrates various engineering computational tools and data storage capabilities. Our NHERI‐SCEC collaboration is focused around the development of data registration, discovery, distribution, and integration of simulated ground motion seismograms into the DesignSafe-CI portal. The broadband ground motion simulations were generated by the SCEC BroadBand Platform (BBP), an open-source computational platform that includes numerous simulation methods. Simulation methods from the BBP have been thoroughly validated and used in such projects as the South Western United States utilities project (SWUS) and the Pacific Earthquake Engineering Research (PEER) Next Generation Attenuation project for Central & Eastern North America (NGA-East). The first subset of seismograms was selected to capture large-magnitude events not currently available in recorded ground motion databases such as those hosted by the PEER center. The seismograms provide ground motions large enough to push structural simulations well into the nonlinear range, providing engineers with the ability to test their models and designs under a wide range of seismic demands. An initial task was to develop a comprehensive flatfile that can accommodate the metadata related to ground motion simulations. The data-discovery tool was developed as a Jupyter Notebook that can be expanded to allow the inclusion of additional ground motion datasets. In this presentation, we introduce the key feature of the flatfile and introduce the interface integrated into DesignSafe-CI.
Slidecast:
https://vimeo.com/278023060
Abstract: A moment tensor is a symmetric matrix that expresses the source for a seismic event. Uncertainty characterization of moment tensors is vital for any interpretation about the moment tensor, such as whether an event is likely to be an earthquake or not. We provide a method for characterizing and visualizing the uncertainty for a full moment tensor. Our uncertainty summary has four components: (1) variation in waveform misfit for the best-fitting moment tensor at each lune point; (2) probability density p(v,w) for moment tensor source type; (3) confidence curve Pcon(V); (4) confidence parameter Pav, which is the area under the confidence curve, with large values representing high concentration of probability near the best-fitting moment tensor. These characterizations are facilitated by a uniform parameterization of moment tensors with fixed magnitude. The parameters describe the source type, with v and w, and the orientation with strike angle, cosine dip angle, and rake angle. The parameterization is uniform in the sense that a uniform distribution of 5-tuples in the coordinate domain corresponds to a uniform distribution in the moment tensor space. Stated otherwise, volumes (i.e. 5-volumes) in the coordinate domain are proportional to the corresponding volumes of moment tensors. Uncertainty in source type and be derived from the probability density p(v,w) in source type, which is depicted easily on the vw rectangular domain. We discuss how this approach could be applied to event screening.
Slidecast:
https://vimeo.com/278017773
Abstract: The eastern North America-Caribbean (NA-CAR) plate boundary near the islands of Hispaniola and Puerto Rico is a complex transition zone in which strain is accommodated by two transform fault systems and oblique subduction. In 2013, scientists from Baylor University, the Autonomous University of Santo Domingo, and the Puerto Rico Seismic Network deployed 16 broadband stations on the Dominican Republic to expand the local permanent network. The goal of the Greater Antilles Seismic Program (GrASP) is to combine its data with that from permanent networks in Puerto Rico, Haiti, Cuba, the Cayman Islands, and Jamaica to develop a better understanding of the crust and upper mantle structure in the Northeastern Caribbean (Greater Antilles). One important goal of GrASP is to develop robust velocity models that can be used to improve earthquake location and seismic hazard efforts. In this study, we focus on obtaining Rayleigh wave group velocity maps from ambient noise tomography. Here we use vertical-component broadband data recorded at 53 stations between 2010 to present, to obtain Green’s functions between 1165 pairs of stations. From these, we obtain dispersion curves by the application of FTAN methods with phase-matched filtering. Group velocity maps are generated between 4 to 40 s. One-dimensional shear wave velocity models are generated for selected sites by convolving group velocity results with depth kernels produced by forward modeling. The Markov Chain Monte Carlo method is applied to estimate the maximum likelihood S wave velocity model and, specifically, Moho depth. Results show strong correlations with large-scale geological and tectonic features for periods between 4 – 40 s, such as the Cordillera Central in both the Dominican Republic and Puerto Rico, the Mona Passage, and the NA-CAR subduction zone. Preliminary 1D shear wave velocity models suggest that the Moho underneath the Dominican Republic and Puerto Rico is in the range of 28 to 32 km.
Slidecast:
https://vimeo.com/278019459
Abstract: The North Anatolian Fault Zone in the Sea of Marmara did not generate a M>7.0 earthquake since 1766. This fault section stores ~20 mm annual slip deficit and therefore is expected to accommodate at least one at most three M>7.0 in near future. In this study, we continuously monitor this critically strained fault section using seismo-geodetic stations that are equipped with 100Hz sampling seismographs and 1Hz sampling GPS recorders. This configuration allows covering a broad spectral band and is sensitive to both fast/slow tectonic motions at large/small temporal and spatial scale, from milliseconds to years, from centimeters to tens of kilometers. Therefore, recorded seismo-geodetic data will be used to identify (1) along-fault variation of the slip deficit, (2) fault segmentation, (3) interaction between slip-deficit and background seismicity, (4) pre-seismic seismo-geodetic symptoms and (5) co-seismic slip in case of M 7.0 earthquake(s).
Slidecast:
https://vimeo.com/278051069
