Abstract: On August 8 2017, an Ms 7.0 earthquake struck the Jiuzhaigou County, Sichuan Province, China. 67 stations of China Strong Motion Network Center (CSMNC) were triggered and recorded ground motions from the event. There were eight stations with epicentral distance less than 100 km of the earthquake. Two temporary stations were installed near station Jiuzhai Zhangzha (JZZ) after the main event. 18 aftershocks with magnitude between 1.2 and 3.9 were recorded from August 19 to August 23, 2017. The largest PGA, greater than 1.0g, was recorded at station JZZ. However, this large ground motion recording is under investigation for possible instrumental or other contaminations. The horizontal peak ground accelerations (PGA) and peak ground velocities (PGV) were obtained and compared to ground motion prediction equation (GMPE) used in the 5th generation of seismic ground motion parameters zonation map of China. The comparisons show that PGAs and PGVs at all stations, except station JZZ are below the GMPE. The S-wave horizontal to vertical spectral ratios (HVSR) were calculated for the main event and aftershocks at station JZZ and the two temporary stations. The results show that the HVSRs at the three sites are quite similar. The HVSRs at station JZZ also show nonlinear site response: the peak frequency shifting from ~10Hz to ~2Hz with amplitude decreasing. Stochastic finite fault source model with dynamic corner frequency was used to simulate ground motions at the eight stations for the main event. The simulated ground motions were compared to the recordings at the eight stations.
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Abstract: At least 75 tsunamis have impacted the region over the last 500 years causing over 3000 deaths. Tsunamis are rapid onset potentially high impact hazards. Due to increasing urbanisation in coastal locales and the low frequency of tsunamis, preparedness and response must be in the psyche of our vulnerable populations to save lives and property. The Tsunami Public Awareness and Education (PAE) Strategy emphasises a mitigation approach in building long-term tsunami awareness and education within the 48 Member States and territories of the Intergovernmental Coordination Group for the Tsunami and Other Coastal Hazards Warning System for the Caribbean and Adjacent Regions (ICG/CARIBE EWS). The strategy is placed within the context of broader international, regional and national disaster risk reduction initiatives, the need for institutional capacity and support, partnerships and shared responsibility across all levels of society to secure resilience. Critical guidance includes audience selection, the effectiveness of multi-media tools and redundant warning dissemination mechanisms, message standardization and increased information flow for successful PAE programming. In recognising the fundamental role of PAE for effective evacuation and warning dissemination to minimise hazard impacts; the Strategy also addresses key synergies between tsunamis and other hazards – earthquakes, landslides, hurricanes and other coastal hazards e.g. coastal flooding and storm surges, which frequently impact the region. These realities of linkages were vividly displayed during the 2017 Atlantic Hurricane season. Regional-level Strategy implementation has largely focused on developing tools for broad audiences, trainings and executing community programmes. Proposed initiatives advance specialised education and sectoral application. The Strategy provides a pioneering, harmonized, regional-level framework for tsunami risk reduction through PAE.
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Abstract: Tall buildings, increasing in number throughout the world, including the Middle East, are greatly affected by long trains of seismic waves from regional earthquakes. Seismic motions, measurable with accurate GPS, are greatly amplified with the increasing height of buildings. Here we show the first successful GPS measurements of the motions of the 414 m tall, Al-Hamra Tower in Kuwait, due to the 11/12/2017 magnitude 7.3 earthquake, 642 km north of Kuwait City on the Iran-Iraq border. The GPS direct measurements of the movements near the top of this building show oscillations of the building, lasting more than ten minutes, with maximum peak-to-peak displacements of 30 cm. The period of the oscillations corresponds to the fundamental mode of the building, and the scalloping nature of the oscillations is produced by the interference of two lowest modes with 7.1 and 5.7 second periods. The large oscillations, occurring in two broad pulses – one and three minutes – after the initial shaking, correlate with GPS and seismic measured ground displacements in the resonance band of the building. GPS measurements show that there was no permanent deformation despite the large swaying of the building. The response of other tall buildings to seismic wave trains can be determined from the seismic power in the resonance band of these buildings and these methods can be applied widely around the world. Measurements of this type with low-cost GPS receivers will soon be possible.
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Abstract: Observations of the wave field at the surface of the Earth are fully characterized at a point by 3 orthogonal vector displacements, 3 horizontal strains, and 3 rigid body rotations. These 9C seismic observables can further be interpreted with a wave propagation model to infer basic attributes of the seismic waves including wave type (from the curl and divergence), azimuth of propagation, and horizontal phase velocity, among other parameters. If these point measurements are then distributed over a surface grid, then images of the wave field and its attributes can be empirically mapped forming tomographic images of the Earth structure effect on the seismic waves. Both the point measurements and expansion into a grid can be made by using dense arrays of seismometers where the seismic observations are incorporated into a finite difference scheme to compute strains and rotations. These kinds of arrays, sometimes called “geodetic” arrays, are becoming feasible to efficiently and cheaply deploy using high frequency (5 or 10Hz dominant frequency) nodal instruments. Accurate computations of strains and rotations from seismic array data depend on precise knowledge of instrument orientations in the field. Estimates of relative amplitude statics and orientations can be made empirically by using teleseismic arrivals simultaneously recorded by the nodal instruments. Two nodal arrays are used to demonstrate the use of gradiometry for inferring wave attributes at a point and over an area. The IRIS Community Wavefields Experiment deployed during June-July 2016 affords a detailed look at instrument orientation and stability for computing wave gradients at a point and for comparison with standard array beamforming techniques. A Large-N experiment consisting of 384 vertical nodal seismometers deployed during an industrial 3D seismic experiment near Utica, Ohio, in 2013 demonstrates the variation of the high frequency wave field over a relatively small area of ~200x300m.
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https://vimeo.com/278571176
Abstract: On December of 2017, already three months after the disastrous hit of Hurricane Maria to Puerto Rico, the president of the Smart Electric Power Alliance said to two E&E News reporters: “Here we are, sadly, in a position where Puerto Rico is as close to a blank slate as we ever thought realistically would come to pass”. The New York Times echoed that statement is a series of articles citing good intentioned citizens saying that this was “a chance to work on a blank canvas”. Since then, more than two dozen U.S. consortiums and renewable energy companies have landed on Puerto Rico looking to implement innovative energy technologies and models in their desire to rebuild the ravaged island. In that process, they have become part of Puerto Rico’s energy debate inside and outside the archipelago. However, the argument of the blank slate is founded on a problematic premise: that energy systems are only physical systems and that they do not involve sociological dimensions such as values, beliefs, institutions, norms and power relationships among stakeholders. In other words, that premise presupposes that energy transitions do not require regime changes, and even if they do, that is accomplished by an injection of new external actors. The Socio-technical Systems (STS) theory has contradicted this premise for more than twenty years. As Verbong and Geels (2006), and Geels (2005), have proposed, socio-technical regimes have at least two main sociological dimensions: actors and formal, normative and cognitive rules. STS also suggests that existing sociotechnical regimes are characterized by path dependence and lock-in, resulting from stabilizing mechanisms on those two dimensions in conjunction with the system’s material and technical elements such as the grid, generation plants, and the energy resources among others (Unruh, 2000; Walker, 2000). This theory can explain why almost five months after the impact of Hurricane Maria, and the influx of many external actors such as FEMA, the US Corps of Engineers, and multinational private companies, more than half of the population is still lacking electric service in the island. It also can illuminate why disaster response and external aid often fails in reaching their goals.
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Abstract: The Mw 8.2 September 8 earthquake occurred in the middle of the “Tehuantepec Gap,” a segment of the Mexican subduction zone that has no historical mentions of a large earthquake. It was, however, not the expected subduction megathrust earthquake, but rather an intraplate, normal faulting event, in the subducting oceanic Cocos plate. We inverted for the slip on the fault plane, using; 1) local strong motion and high rate GPS records and 2) teleseismic body and surface waves, together with static GPS offsets. From the hypocenter at a depth of 50 km, the rupture propagated NW on a near-vertical plane, breaking towards the surface. Most of the slip was concentrated in the distance range 30-100 km from the hypocenter and at depth between 15 and 50 km, with maximum slip of ~15m. The earthquake seems to have broken the entire lithosphere, estimated to be 35 km based on the plate age. The strike of the fault is sub- parallel to the trench, aligned with the existing fabric on the incoming plate, suggesting a reactivation of previous structures. We relocated the aftershocks and found that they occurred along the fault plane during the first day after the event, with activation of other parallel structures within the subducting plate, towards the east, as well as in upper plate, in the following days. Coulomb stress modeling suggests that the stress on the plate interface, updip of the earthquake, is reduced. There are several other examples of large intraslab normal faulting earthquakes, near the downdip edge (1931 Mw 7.8 and 1999 Mw 7.5, Oaxaca) or directly below (1997 Mw 7.1, Michoacan) the coupled plate interface, along the Mexican subduction zone. The possibility of events of similar magnitude to the 2017 earthquake occurring close to the coastline, all along this part of the subduction zone, cannot be ruled out.
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