Abstract: Ecuador is a zone of high volcanic seismicity, in such sense it is important to recognize the behavior of volcanoes before they enter into an eruption process. This requires the analysis and to identification of different types of seismic events from a volcano. Cotopaxi volcano, is one of the most active and it has high risk due to the close proximity of populated areas in its surroundings and therefore it is one of the most supervised volcanoes in Ecuador. In this paper, a review of the most used spectral techniques for the analysis and extraction of discriminant features of microseisms is presented, since microseisms are some of the most important sources of information for analyzing the behavior of different volcanoes. Hence, our aim is to extract spectral features, which may help to classify events correctly, this information may also allow authorities to give early alerts in the case of increasing volcanic activity in order to alert and safeguard human lives. The analysis is performed by using parametric and non-parametric spectral techniques, enabling a more detailed study of the spectral content and the confidence intervals of specific events by using bootstrap technique, the empirical bootstrap procedure was specifically used, this consists in resampling the data from the empirical distribution. A database from the Cotopaxi volcano corresponding to a single station, with a broadband seismometer, containing several seismic signals representing different types of volcanic events such as volcano-tectonic (VT), long period (LP), hybrid (HYB) and tremors (TRE) registered in 2012, was used for the analysis. The results obtained show that LP events have a thin spectrum and their frequency range goes from 0.5 Hz to 6 Hz, with a major spectral component around 3.2 Hz, VT events have a wide spectrum and their frequency range goes up to 20 Hz with a major spectral component around 6.8 Hz, and TRE events have a spectrum that goes below 3 Hz.
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Abstract: Beginning in 2016, the USGS started to produce one-year PSHA models to account for the elevated seismicity in this region mainly due to the wastewater injection. We assess the full 2016 model by comparing the model forecast with the observed instrumental ground motions in PGA and spectral response acceleration for 1hz and 5Hz over the entire CEUS. Our results indicate that the observed hazard is generally consistent with that forecast by the model. Our results show that for mapped hazard level (1% probability of exceedance in one year) and using only one year of observation, is unlikely to reveal the inconsistency between the observed and forecasted hazards with high confidence due to the low number of earthquakes CEUS. We also explore the variability in 2016 and 2017 models due to epistemic uncertainty in its informed submodel. We find that variability is highest in low seismicity areas. Average variability increased in the 2017 one-year model relative to 2016 model. The highest hazard variation in the final model is associated with different ground motion models and maximum magnitudes used in the logic tree, while the variability due to the smoothing distance is minimal.
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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: We are developing a new seismic hazard model for Mainland China by integrating historical earthquake catalogs, geological faults, geodetic GPS data, and geology maps. To build the model, we construct an Mw-based homogeneous historical earthquake catalog spanning from 780 B.C. to present, create fault models from active fault data, and derive a strain rate model based on the most complete GPS measurements and a new strain derivation algorithm. We divide China and the surrounding regions into about 20 large seismic source zones. For each zone, a tapered Gutenberg-Richter (TGR) magnitude-frequency distribution is used to model the seismic activity rates. The a- and b-values of the TGR distribution are calculated using observed earthquake data, while the corner magnitude is constrained independently using the seismic moment rate inferred from the geodetically-based strain rate model. Small and medium sized earthquakes are distributed within the source zones following the location and magnitude patterns of historical earthquakes. Some of the larger earthquakes are distributed onto active faults, based on their geological characteristics such as slip rate, fault length, down-dip width, and various paleoseismic data. The remaining larger earthquakes are then placed into the background. A new set of magnitude-rupture scaling relationships is developed based on earthquake data from China and vicinity. We evaluate and select appropriate ground motion prediction equations by comparing them with observed ground motion data and performing residual analysis. To implement the modeling workflow, we develop a tool that builds upon the functionalities of GEM’s Hazard Modeler’s Toolkit. The GEM OpenQuake software is used to calculate seismic hazard at various ground motion periods and various return periods. To account for site amplification, we construct a site condition map based on geology. The resulting new seismic hazard maps can be used for seismic risk analysis and management.
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Abstract: We present an updated compilation of earthquake focal mechanisms (FM) in Brazil together with the sub-Andean region through more obtained solutions together with published results from the literature and international agencies catalogs. Stress orientations from breakouts and in-situ measurements were also compiled. For Brazil, we have 88 earthquakes with the FM determined since 1978. They show reverse, strike-slip and normal faulting while events in the sub-Andean region have reverse (majority) or strike-slip FM. For sub-Andean region have reverse (majority) or strike-slip FM. Normal FM can be found only in high attitudes. The FM were grouped by proximity to be inverted for the stress tensor. In SE Brazil and the Chaco-Pantanal basins, S1 tends to be oriented roughly E-W with S2 approximately equal to S3. This stress pattern changes to purely compressional in the São Francisco craton. A rotation of SHmax from E-W to SE-NW is suggested towards the Amazon region. Along the Atlantic margin, the regional stresses are affected by coastal effects. This coastal effect tends to make SHmax parallel to the coastline and Shmin (usually S3) perpendicular to the coastline. Breakout data and in-situ measurements are available are generally consistent with the pattern derived from the FM. In the sub-Andean region, the intermediate principal stress (S2) is also compressional, a feature that is not always reproduced in numerical models published in the literature. In mid-plate South America stresses seem to vary in nature and orientation. Although numerical models of global lithospheric stresses tend to reproduce the main large-scale features in most mid-plate areas, the S1 rotation from E-W in SE Brazil to SE-NW in the Amazon region are not well explained by the current numerical models. This means that the observed stress pattern in mid-plate South America should provide new insights into upper mantle dynamics, distinct from current global convection models.
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Abstract: The Source Physics Experiment (SPE) is an ongoing effort to improve explosion monitoring by conducting a controlled series of chemical explosions at the Nevada National Security Site (NNSS) and using the resulting observations to improve and validate physics-based simulations of explosion phenomena. Phase I of SPE was conducted on the Climax Stock granite which contains a network of well-characterized joints. It has been shown that these pre-existing joints may be responsible for the tangential motion observed during SPE chemical explosions. Near-field motions generated with hydrodynamic non-linear source models have been coupled to elastic wave propagation codes to propagate these resulting motions into the far-field domain which is assumed to be elastic and isotropic. This is likely not the case as the pre-existing joints continue beyond the inelastic source region of the explosion. To alleviate this impediment, we extend the current near-field to far-field, hydrodynamic-to-elastic coupling, from anisotropic-isotropic to fully anisotropic-anisotropic coupling. Near source hydrodynamic motions are computed using GEODYN-L while anisotropic elastic wave propagation is modeled using SW4. Motions are coupled between the two codes by introducing hydrodynamic motions from GEODYN-L as an internal boundary source to SW4. The anisotropic material model employed in the SW4 domain is derived from the properties of an observed fracture network with relatively well-constrained joint size, density, orientation, and aperture. We show that consideration of anisotropic material in the elastic regime has an important effect on the propagation of tangential motion. Propagation of motions generated in an anisotropic source region into an isotropic far-field domain may hinder the continuity of the waves in general and may impede the shear motion generation. Prepared by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-744746.
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