Abstract: Pseudo-spectral acceleration (PSA) is the most commonly used intensity measure in earthquake engineering, as it serves as a simple approximate predictor of structural response for many types of systems. Therefore, most ground motion models (GMMs, aka GMPEs) provide median and standard deviation PSA using a suite of input parameters characterizing the source, path and site effects. Unfortunately, PSA is a complex metric: the PSA for a single oscillator frequency depends on the Fourier amplitudes across a range of frequencies. The Fourier Amplitude Spectrum (FAS) is an appealing alternative because its simple linear superposition allows effects to be modeled as transfer functions. For this reason, most seismological models (e.g., the source spectrum) are developed for the FAS. Using FAS in conjunction with random vibration theory (RVT) allows GMM developers to superimpose seismological models directly, computing PSA only at the end of the process. The FAS-RVT-PSA approach was used for the development of GMMs for the Next Generation Attenuation Relationships for Central & Eastern North-America (NGA-East) project [PEER, 2018]. As part of the project, the team above developed a systematic processing algorithm for FAS that minimizes computational requirements and bias that results from the RVT approximation. We introduce the down-sampled orientation-independent FAS referred to as the effective amplitude spectrum (EAS) and recommended it as a new approach for characterizing the frequency content of ground motion records. This algorithm down-samples the EAS with a Konno and Ohmachi [1998] smoothing window with a width (bw) of 1/30 and 100 frequency points per decade. This smoothing window was identified as having the least impact on a suite of RVT calibration properties. We applied this smoothing to the FAS delivered through the PEER ground motion portal for NGA-East and NGA-West2 databases.
Poster:
WED.Monroe.1645.Goulet
Abstract: Two large normal faulting intraslab events occurred in rapid succession in Mexico in 2017, the 8th September M8.2 Tehuantepec, and 19th September M7.1 Puebla-Morelos earthquakes. Here we will discuss detailed source models of both earthquakes produced from inversion of all available regional geophysical data. This includes, strong motion, high-rate GPS, static GPS, tide gauge, and ocean-bottom pressure data. Although the commonly accepted hypothesis for intraslab earthquakes is slab dehydration, we show that for both events also pre-existing seafloor fabric plays a determining role. During the Tehuantepec earthquake, the chain of events is that a bend fault first formed from reactivated fabric in the outer rise rotates through the megathrust and, with help from wholesale deviatoric tension and strong slab pull, hosts the normal faulting event. The earthquake ruptured from the megatrhust down to the edge of the lithosphere, and we find robust evidence that embrittlement is much deeper than previously thought and extends to temperatures as high as 1100°C. Similarly during the Puebla-Morelos intraslab event we find that bend faulting at the edge of the flat slab segment hosts the normal faulting event. Similarly we show from an analysis of the seafloor morphology that abyssal hill fabric formed during seafloor spreading and advected through the subduction system, represents a key pre-existing weakness plane that promotes the intraslab event. Sharp bending as the flat slab unfurls into the mantle produces a substantial bending moment placing the top half of the subducted lithosphere under flexural extension.
Slidecast:
https://vimeo.com/277697960
Abstract: An international task force is working to integrate environmental monitoring sensors into submarine telecommunication cables. The SMART Cables Initiative – for Science Monitoring And Reliable Communications – is sponsored by several UN agencies and led by the Joint Task Force. The SMART cables concept calls for adding sensor suites to the repeaters of future submarine cables, which are spaced at intervals of 50-75 km along the ocean floor. Initially, temperature, pressure, and acceleration sensors will be integrated, with expanded capabilities in planning. As cables are replaced and expanded, this would create a global deep ocean sensor network capable of sustained, cost-effective data collection in the deep ocean to addresses two critical needs for science and society: 1) the near term need for improved resolution and rapidity in global tsunami warning and seismic monitoring, and 2) the long term need for sustained, cost-effective ocean and climate data from the deep oceans. The acceleration sensors will pick up strong ground motion from nearby earthquakes; recent instrumentation improvements allow sensing smaller or distant earthquakes. The inclusion of seismic sensors opens a new window of opportunity; we provide a discussion of the solid Earth modeling and expected ocean bottom seismology impacts of the initiative. The initiative has won endorsement from numerous scientific organizations, and modeling studies are underway to quantify the expected benefits of the improved sampling. The initiative, currently moving from the concept stage into prototyping, has the potential to provide a first order addition to the ocean and Earth observing system, with unique contributions that will strengthen and complement existing systems. See Joint Task Force (JTF), ITU/WMO/IOC SMART Cables for Observing the Ocean
Slidecast:
https://vimeo.com/277703501
Abstract: Science gateways are Web interfaces and middleware that both simplify access to supercomputers and expand the capabilities of their users through graphical user interfaces. Since initially conceived two decades ago, science gateways have matured into production services used daily by many scientists. For example, science gateway users of XSEDE supercomputers consistently outnumber regular command line users, and users of Galaxy (a bioinformatics gateway) and NanoHUB (a nanotechnology gateway) number in the tens of thousands. We believe there is a need and an opportunity to dramatically increase the use of gateways and related cyberinfrastructure in earthquake science. This can be done in three related ways: by simplifying access to popular modeling and simulating tools, by providing better mechanisms for interacting with data products such as InSAR and GPS data, and by enabling novel applications of machine learning technologies that are outside the expertise of many geoscientists to geophysical data sets. In this talk we introduce general science gateway concepts, provide an overview of the NASA-funded GeoGateway project, and describe how GeoGateway will evolve as we align it with the Apache Airavata framework for science gateways. We are developing GeoGateway as a means for geoscientists to access, integrate, and share multiple data sets, including InSAR, GPS, seismicity, and optical data. GeoGateway provides more than access to data sets: by coupling data to modeling and simulation codes, it enables users to easily incorporate data into their computational experiments. Looking forward, we also see important opportunities for coupling data to a range of machine learning techniques that can be used to identify features in data sets that are not readily discernible by human inspection. It is important to develop GeoGateway’s capabilities within a general framework in order that we can take advantage of features already available from other science gateways. At the same time, GeoGateway has unique or forward-looking capabilities compared to many gateways, so innovations made by GeoGateway can be contributed back to open source science gateway frameworks. We thus describe the synergies between GeoGateway and the Apache Airavata framework for building science gateways, and how Apache Airavata can be used to build other science gateways.
Slidecast:
https://vimeo.com/278017506
Abstract: On January 10, 2018 at 2h51 UTC (January 9 between 8:51 and 10:51 PM local time) a Mw 7.6 earthquake occurred offshore Swan Island (Honduras). Fortunately there was no significant damage from the earthquake and the tsunami was small. This was the first time the Pacific Tsunami Warning Center (PTWC) issued a Tsunami Threat for the Caribbean since the enhanced tsunami products for the UNESCO IOC Tsunami and Other Coastal Hazards Warning System for the Caribbean and Adjacent Regions (CARIBE EWS) were adopted in 2015. It was also the first time a Tsunami Advisory was issued for Puerto Rico and the US and British Virgin Islands (PR/VI). While the first message that was issued was based on the earthquake, following messages integrated the tsunami forecast and observations. The earthquake was felt in some countries; others for whom the Tsunami Threat/Advisory was issued did not report feeling the earthquake which is often the first sign of a potential threat, making even more important the official alerting process. Both the international and domestic text products were timely sent by the PTWC to designated authorities and posted on the tsunami.gov website. For the international stakeholders it is their responsibility thru their designated Tsunami Warning Focal Point/National Tsunami Warning Center to determine the threat level. In the case of PR/VI, the alert level (Warning, Advisory, Watch or Information) is established by the PTWC. In either case, international or domestic, it is the responsibility of the national/local governments to decide on the actions to be taken (evacuate or not evacuate) and to notify the public. The event timeline, as well as the UNESCO IOC CARIBE EWS after action report will be presented. In addition to identifying the strengths and gaps of tsunami warning system, the event review is also important considering the impact that hurricanes Irma and Maria had on local communication and emergency response systems and the public.
Slidecast:
https://vimeo.com/277700711
Abstract: The Las Vegas Valley fault system (LVVFS) is a complex set of north- to northeast- trending, intra-basin Quaternary fault scarps up to 30 m high that displace alluvial fan, fine-grained basin fill, and paleo-spring deposits in the densely populated Las Vegas metropolitan area. Characterizing the seismic hazard of the LVVFS is currently the focus of a multi-year collaborative study involving researchers from the Nevada Bureau of Mines and Geology, University of Nevada, Las Vegas, and the U.S. Geological Survey. The Eglington fault is the only LVVFS fault currently included on the National Seismic Hazard Map (NSHM), and is a priority focus in the early stages of the investigation. Substantial uncertainty remains regarding the seismogenic potential of the LVVFS. Two endmember hypotheses have been proposed regarding the mechanisms responsible for producing the scarps associated with the LVVFS, including the Eglington fault: 1) tectonic (e.g., coseismic surface rupture) and 2) non-tectonic (e.g., prehistoric differential sediment compaction). In this presentation, we will summarize existing geologic, geodetic, geophysical, and geochronologic data that provide insight into the mechanism(s) responsible for scarp formation within the LVVFS, and present unresolved problems with both endmember tectonic and non-tectonic scenarios. We will also discuss in-progress efforts to characterize the seismogenic potential of the Eglington fault including: planned paleoseismic trenching, geologic mapping using lidar and predevelopment topography derived from historical aerial photographs, Optically Stimulated Luminescence (OSL) dating of the Las Vegas basin stratigraphy, and evaluation of the potential for differential sediment compaction across the fault scarps. In addition, we will present the recommendations from the 2018 Working Group on Nevada Seismic Hazards, including the details of a logic tree framework to address uncertainty in the LVVFS hazard assessment.
Slidecast:
https://vimeo.com/277703108
