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 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: 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: 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: Following the discovery of the Shoreline Fault along the coast of central California by Hardebeck (2010) and the occurrence of the tsunami disaster at the Fukushima nuclear power plant in 2011, there has been increased attention on the potential seismic hazards of the central California region in relation to the Diablo Canyon nuclear power plant. The Pacific Gas & Electric Company has supported related research both offshore and onshore, and the Southern California Earthquake Center (SCEC) has established a Central California Seismic Project (CCSP) to develop a Community Velocity Model (CVM) and Community Fault Model for the region and use them for strong motion simulations and hazard estimation. The existing SCEC Central California CVM was developed from a USGS velocity model, velocity measurements from wells and seismic surveys, and refinement using waveform tomography. We are working to further refine the Central California CVM by (1) incorporating surface-wave dispersion data from an expanded set of stations and extended to shorter periods (3 to 4 seconds) and (2) incorporating body-wave arrival-time data from earthquakes and P-wave travel times from explosions. The current SCEC Central California CVM will be used as the starting model for new surface-wave inversions, new body-wave inversions, and ultimately joint body wave-surface wave inversions. Inversions using the new data will result in a finer resolution CVM for central California. Research supported by SCEC Award #17188 and USGS Award G16AP00111.
Slidecast:
https://vimeo.com/278026457
Abstract: The Cordillera Blanca batholith is an intrusive emplacement of Miocene age (5 Ma) that lies over the northern-central Peruvian Andes. Its western flank is bounded by a normal fault that extends for about 220 km in a NW-SE direction and dips west at a low angle. There is no historical evidence of large earthquakes associated with this fault, but geological studies indicate Quaternary or Holocene activity with as much as 2.5 m of vertical slip. Other related events in the neighborhood of the Cordillera Blanca Fault are the 1942 Quiches (M 6) earthquake and the 1970 Chimbote earthquake (Mw 8). The Chimbote event caused the highest death toll of all times in Peru (70,000 casualties) as it triggered a massive mudslide that swept all along its path and buried the town of Yungay. The ice-and-snow covered, elevated peaks (up to 18,000 ft.) in the Cordillera Banca mountains, as well as the existance of the active bounding normal fault system, represent a big hazard to this region. This study presents the first geodetic estimates of the modern kinematics of the Cordillera Blanca Fault and uses GPS measurements carried out between 2014 and 2017, as well as baseline changes observed between two cGPS stations across its southern end.
Slidecast:
https://vimeo.com/278051014
