Abstract: UNAVCO streams data from ~800 real-time, GNSS sites (RT-GNSS) from a combination of NSF-sponsored networks that together span large segments of the North American-Pacific plate boundary, the EarthScope Plate Boundary Observatory (PBO), the Caribbean plate boundary (COCONet) and Mexico’s Pacific plate boundary (TLALOCNet). Raw data streams are transmitted from the remote GNSS sites to UNAVCO’s data operations center where Precise Point Position (PPP) estimates are generated and distributed in real-time. Recent work has shown that GNSS-defined peak ground displacements (PGD) provide a magnitude scaling relation that, unlike estimates based on the first seconds of the P-wave, does not saturate above M7. The inclusion of RT-GNSS PGD data can therefore greatly enhance the accuracy of early warning systems by providing improved magnitude estimates of large earthquakes. To take full advantage of this, not only must the data be complete and low latency, but it is essential that the PPP estimates have sufficiently low noise-levels such that long-period surface waves can be detected in real-time. Here, we show that we can combine the ambient noise levels in the GNSS PPP solutions with the GNSS-derived PGD scaling relationship to assess the ability of the PBO, TLALOCNet and COCONet networks to unambiguously detect the long-period surface waves generated by large earthquake events. This enables implementation of tools for evaluating and continuously monitoring the capability of magnitude-threshold detection level for RT-GNSS networks. We find that with the current network configuration, RT-GNSS PGD would be detectable for most UCERF3-defined faults in California but this capability is decreased for events along sections of the Cascadia and Mexican Pacific plate boundaries.
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Abstract: The seismic and acoustic activity of the Colima Volcano is studied and monitored by the Seismic Network of the State of Colima (RESCO), which belongs to the University of Colima. Nine broadband stations around the volcano record seismic activity in real time. Additionally, an acoustic sensor installed by the UNAM near the seismic station of Montegrande recorded the most important explosions in January and February 2017. The seismic-acoustic monitoring includes the location of volcano-tectonic events (VTs), explosions, rockfalls, count of events automatically with Hidden Markov Models, evaluation of the seismic and acoustic energy of the explosions, RSEM, etc. In recent years (2013-present), the activity of the volcano has been intense, lava domes growths, lava flows, lava dome collapses, as well as moderate to large explosions. Particularly the explosions in 2017, in their acoustic signals had a characteristic waveform of ‘N’. The seismic energy observed in the explosions had values above 1e + 8 Joules, while that the acoustic energy only presented 5 explosions that exceeded this value. With these values the ratio between acoustic and seismic energy remained mostly less than 1. This indicates that the seismic-acoustic source is probably generated in a long and narrow conduit, likewise, the volcanic columns were charged with ash according to the models of Johnson and Aster (2005). Similarly, the time between the arrival of the seismic wave and the acoustic wave is observed between 15.6 to 19.6 sec, which tells us that there are a small variation in the depth of the source. These explosions are lower in the seismic energy released compared to the 2005 activity.
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Abstract: An unusual, ongoing, earthquake swarm is currently active in a non-volcanic area in western Saudi Arabia near the town of Umm-Lujj. Since February 2017, hundreds of earthquakes have been recorded continuously, with a maximum magnitude reaching MI 3.7. Although this earthquake swarm occurs only about 75 km NW of the volcanic area of Harrat Lunayyir, it does not appear to be directly associated with it. The latter experienced a magmatic dike intrusion in 2009 with intense seismic activity (including a surface rupturing Mw 5.7 earthquake). We use seismological data, recorded by the Saudi Geological Survey (SGS) that operates 45 broadband seismic stations. We analyze the continuous seismic waveform data provided by the SGS broadband stations to map the spatial and temporal distribution of seismicity in an effort to gain insights on the underlying physical processes that are responsible for this swarm. We use double-difference algorithm to determine the relative distances between earthquakes. The relocation results using both P- and S- phases greatly improve the earthquake locations. We identified 3 events clusters, each at a different depth level. These clusters are concentrated within a well-defined rock volume of roughly 10 km3. The dominant cluster of these events is shallow (4-8 km depth). The deepest cluster includes events occur as deep as 16 km. The results may reveal an image of the NW-SE Najd fault system (a complex set of strike-slip faults and shear zones across the Precambrian of Arabia). Using the well-relocated events, we assemble the body wave arrival times that are inverted for the local velocity and attenuation models. The focal-mechanism solutions of the largest earthquakes (> Ml 2.0) vary widely, indicative of a highly fractured complex fault system and without a clear correlation to the regional stress field of Red Sea. This observation is in agreement with the complex local tectonics of the shear system which accommodates the swarm sequence.
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Abstract: The objective of the Fault to Seismic Hazard Assessment (Fault2SHA) Working Group is to build a community of active fault-related researchers to exchange data, tools and ideas on how to best model faults in seismic hazard assessment in specific tectonic contexts. After a few meetings (Paris 2014, Chieti 2015) and thematic sessions at international conferences in 2016 (https://sites.google.com/site/linkingfaultpsha/home) the WG was officially established inside the European Seismological Commission (ESC) in 2016. Being a not-funded entity the WG acts on voluntary basis. The community involved is made of data providers, data modellers and data users willing to share data and methodological approaches. The WG milestones achieved since 2016 are: a paper on aftershock probabilistic seismic hazard based on fault data gathered by many European teams in the wake of the Amatrice, 2016 M6.0 earthquake (Peruzza et al., 2016); the organisation of an international workshop in Barcelonette in 2017, France, that gathered 50 participants from around the world; the publication of 10 papers in a special issue of the NHESS journal; the organisation of a training course in Paris in 2017, where geologists learned how to use some Fault2SHA tools. The WG has initiated other collaborative initiatives such as the establishment of natural laboratories in Italy and Spain. Preliminary results will be presented at SSA. In these laboratories we want to address specific issues and questions such as: Methods to define sections/ruptures; Physics-based approaches; Needs for the collection of data (volcanic area?) to update scaling laws; How to constrain slip on faults using geodesy? How to propagate uncertainty in fault-PSHA? The Fault2SHA session to be held during the 2018 SSA conference in Miami is an additional opportunity to widen the discussion beyond the European context and to open to new potential members the opportunity to join us at the next ESC meeting that will be held in 2018 in Malta.
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Abstract: The TEMPP project in Honduras was a project designed to start from scratch until it created the local and regional capacities needed to prepare coastal communities for tsunami events. Two communities were chosen for this project, the community of Sambo Creek on the coast of the Caribbean Sea in northern Honduras and the community of Cedeño on the Pacific coast. After several deliberations, it was agreed that only the project in Cedeño would be worked on. TEMPP1 was a workshop whose fundamental purpose was to transfer the basic tool of tsunami modeling, in this case the program called COMMIT, to the specialists and technicians who would be responsible for modeling tsunami waves that could affect the communities previously chosen in the project. Multiple scenarios were modeled for the communities and those scenarios that represented the greatest danger were selected for subsequent analyzes. Under TEMPP2, national, regional and international experts in geology and seismology were brought together for the purpose of exchanging experiences and information on possible sources capable of generating tsunami waves. Various sources on historical tsunamis registered in the region were reviewed as well as geological and seismological information in order to characterize the sources in the best possible way. During the TEMPP3 the training on GIS was carried out for the elaboration of the evacuation map, also the field visit was made to georefy all the relevant places such as schools, hospitals, fire stations, police stations, etc. to be included in the evacuation map. TEMPP4 was the workshop where the parameters for the simulation were established. The criteria were discussed and procedures were socialized with the different actors that would participate in the simulation. TEMPP5 was the realization of the simulation by tsunami for the community of Cedeño in the pacific coast of Honduras. The local police, fire brigade, schools, hospitals, etc. were involved. At the end of the drill, an evaluation was carried out by UNESCO in order to determine if the community met the requirements to be considered prepared for tsunami events. Finally, it was declared that this community was ready and it was certified as “tsunami ready”.
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Abstract: A more realistic representation of the geologic subsurface assumes the rock behaves as an orthorhombic elastic medium as opposed to an isotropic elastic medium, which is commonly done. An orthorhombic medium is characterized by three mutually orthogonal symmetry planes comprising a dense system of vertically-aligned microfractures superimposed on a finely-layered horizontal geology. Mathematically, the elastic stress-strain constitutive relations for an orthorhombic body contain nine independent moduli. We are developing an explicit time-domain finite-difference (FD) algorithm for simulating three-dimensional (3D) elastic wave propagation in a heterogeneous orthorhombic medium. The particle velocity vector and the stress tensor are governed by a set of nine, coupled, first-order, linear, inhomogeneous partial differential equations. All time and space derivatives in this system are discretized to achieve second-order and fourth-order numerical accuracy, respectively. Novel perfectly matched layer (PML) absorbing boundary conditions, specifically designed for orthorhombic media, are also implemented. This FD code is used to support the modeling component of the Source Physics Experiment (SPE), a series underground chemical explosions at the Nevada National Security Site. The data from the experiments are used to help determine event signatures that vary depending on geology, yield and depth of burial. We present simulations of the SPE Phase I series using our orthorhombic FD code and the subsequent comparison to the recorded data. These comparisons are used to calibrate the source and will be used for subsequent pre- and post-experiment modeling of SPE Phase II. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
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