Abstract: The USArray project represents a once-in-a-generation opportunity to fundamentally change geophysical monitoring in the US Arctic. The addition of more than 200 stations capable of recording seismic, infrasound, ground temperature and meteorological data has brought a diverse group of organizations to the table, fostering new connections and collaborations between scientists whose paths otherwise would not cross. With the array slated for removal beginning in 2019, there is a window of opportunity to advocate for permanently retaining a subset of the USArray stations. The Alaska Earthquake Center has drafted a plan to permanently adopt a subset of the USArray stations and maintain them as part of the seismic network in Alaska. The expanded seismic network would substantially improve on the Alaska Earthquake Center’s ongoing mission to advance Alaska’s resilience to earthquake hazards. The many challenges in adopting USArray stations include choosing which stations to retain, upgrading the power systems to have 24/7 data transmission through the long Alaskan winter months, and lowering the costs of continuous telemetry. The final station selection will also carefully consider the needs of partner organizations, since the USArray network currently fills important gaps in the weather, wildfire and climate research monitoring networks across Alaska.
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Abstract: We present a preliminary model to systematically quantify the long-term earthquake risk of over six hundred thousand bridges located throughout the conterminous United States. The model uses (1) the 2014 U.S. Geological Survey’s long-term earthquake shaking hazard model, (2) the 2017 National Bridge Inventory (NBI) data available through the Federal Highway Administration (FHWA), and (3) earthquake fragility/vulnerability relationships for bridges available through the Federal Emergency Management Agency’s (FEMA) Hazus program. Each year, the FHWA compiles bridge inventory data from US states, federal agencies, and tribal governments. These agencies compile comprehensive details as part of the bridge inspection process in accordance with the National Bridge Inspection Standards. The NBI dataset contains the most up-to-date stock of the nation’s bridges, and lists a number of attributes pertaining to each bridge structure, such as, location, year built, bridge type, number of spans, length, skew, and inspection date. We use these attributes to categorize each bridge into a model structure type category, for example, using the Hazus Bridge Classification Scheme for vulnerability and risk analyses. For each bridge site, we first obtain an earthquake shaking hazard curve defined in terms of spectral acceleration (Sa) at a spectral period of 1.0 sec, and then integrate it with the bridge-specific fragility curve to compute long-term earthquake risk. Attributes such as the skewness and number of spans are accounted for in the evaluation of damage potential through fragility relationships from FEMA’s Hazus methodology for damage/risk assessment. Earthquake risk herein refers to a probability of experiencing slight, moderate, extensive, or complete damage states during the useful life of each bridge structure. In this presentation, we summarize some key findings and discuss potential improvements to these preliminary assessments.
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Abstract: We investigated microseismicity, geodetic slip and structural setting along the western North Anatolian Fault NAF to characterize their influence on pre-, co- and post-seismic stages of the 2014 North Aegean Earthquake (M 6.9). We identified that the NAF in North Aegean Sea (NAS) operates beneath three basins and two transpressional ridges rather than a single through-going basin. Refined hypocenters indicate that NAF is a narrow shear-zone in the east, and systematically expands towards the west. Microseismicity has a wide spread epicentral pattern at pre-seismic stage of the 2014 earthquake, but later tightens during post-seismic stage. This suggests that pre-seismic strain accumulation was completed on the main fault and transferred to surrounding secondary structures, and the slip returns back to the main fault following the mainshock. Overall microseismicity pattern shows that seismogenic zone becomes deeper to the west and shallower to the east. Three fault segments merged with two step-overs have failed during the 2014 North Aegean Earthquake rupturing a ~90 km section of the NAF. There, co-seismic slips reach up to ~80 cm beneath western step-over and remains below ~60 cm beneath eastern step-over. Along-fault pre- and co-seismic slips show a complementary pattern verifying that the 2014 mainshock generated the highest slip at pre-seismically locked patches, located beneath transpressure ridges hosting two step-overs. High pre-shock concentrations underneath suggest fracturing at seismogenic basement overcoming frictional strength at these two fault step-overs.
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Abstract: The subduction zone in Mexico has unique characteristics as compared to the other subduction zones in the western and eastern Pacific. In Mexico, the scale appears to be a two-to-one size compared to other subduction regimes. The distance from the trench to the coast and the average thickness of the continental lithosphere, above the locked interplate zone, is half of what is observed in other regions. The comparison between Mexico and Peru and Central Chile, where the slab also subducts sub-horizontally, clearly demonstrates this scaling. The result of this unique tectonic structure is that the maximum depth of seismogenic coupling in Mexico, as shown by geodetic studies and aftershock observations, is only 20 km deep, as opposed to the width of the interplate contact of up to 50 km observed in other subduction zones. The width of the locked interplate zone appears to be the limiting factor on the size of the largest earthquakes generated along the Pacific coast of Mexico. A comparison of great subduction earthquakes in Mexico and South America clearly brings out that the Mexican subduction zone has earthquakes that normally are not greater than Mw 8.1. In contrast, during the instrumental period of almost 120 years, South America has suffered much more frequent and larger events (Mw > 8.6). The reason may be the anomalously thin lithosphere of the continental plate, overlying the megathrust plate contact. Although earthquakes as large as Mw 8.6 are present in the Mexican subduction zone, as interpreted from the historical records, these great earthquakes are infrequent. Thus the average magnitude of large earthquakes appears to be controlled by the narrow seismogenic zone resulting from this unique tectonic environment. This limit on the size of great earthquakes in Mexico is important for the estimation of seismic risk in the region.
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Abstract: MSNoise is an Open and Free Python package known to be the only complete integrated workflow designed to analyse ambient seismic noise and study relative velocity changes (dv/v) in the crust. It is based on state of the art and well maintained Python modules, among which ObsPy plays an important role. To our knowledge, it is officially used for continuous monitoring at least in three notable places: the Observatory of the Piton de la Fournaise volcano (OVPF, France), the Auckland Volcanic Field (New Zealand) and on the South Napa earthquake (Berkeley, USA). It is also used by many researchers to process archive data, e.g. focussing on fault zones, intraplate Europe, geothermal exploitations or Antarctica. We first present the general working of MSNoise, originally written in 2010 to automatically scan data archives and process seismic data in order to produce dv/v time series. We demonstrate that its modularity provides a new potential to easily test new algorithms for each processing step. For example, to experiment new methods of cross-correlation (done by default in the frequency domain), stacking (default is linear stacking, averaging), or dt/t or dv/v estimation (default is moving window cross-spectrum “MWCS”, so-called “doublet”), etc. Finally, we present the last major evolution of MSNoise, from a “single workflow: data archive to dv/v” to a framework system that allows plugins and modules to be developed and integrated into the MSNoise ecosystem. Examples of plugins in development such as continuous PPSD (à la McNamarra & Buland) or ambient noise tomography (ASNWT) will be presented. This poster will also present the latest developments of ObsPy and applications using it.
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Abstract: To resolve the problem of ground motion observation which lead to the widespread concern in the field of seismic engineering, this study provided a non-contact ground deformation testing method based on vision technology and numerical simulation. Studies are carried out on key technologies of this dynamic ground deformation testing system, such as the vision data of target in real time which is acquired by the visual testing technology was automatically analyzed, using the obtained relative displacement as the bond quantity which is continuously iterated through the numerical simulation system to finally output the more accurate absolute displacement of the ground surface. The result shows that the precision of measurement can get to mm which meets the accuracy requirements of ground motion monitoring, and the accuracy and feasibility of visual testing technology is verified. The test method not only fills in the blank of the real-time monitoring instruments for ground displacement during the earthquake, but also provides more accuracy and wider range of data for the research on seismic source and fault information inversion and recognition of the ground motion characteristics.
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