Abstract: The NGA-Subduction project is currently under development, focusing on analyzing the collected data for different regions affected by subduction-zone earthquakes around the world. As part of this effort, an earthquake-source database has been developed for events with ground motion recordings obtained in Chilean territory. Data from the South American subduction zone, and particularly from Chilean earthquakes, are critical for the success of this project, due to the availability of data from many large (M > 7.5) interface subduction events and the importance of significant regional path effects previously observed in Chile but not evident elsewhere. The source database contains information on seismic moment, moment magnitude, hypocenter location, nodal planes, and fine-fault geometric parameters. More than 40 different finite-fault models have been collected and evaluated, introducing a uniform and consistent procedure for fault trimming, where only the trimmed portion of the fault plane with significant slip is used for source-to-site distance calculations. For events that lack published finite-fault models, uniform protocols are applied to assign the source parameters and a simulation-based representation of the finite-fault parameters is used for distance calculation. To support the use of these simulations for subduction-zone earthquakes, relationships for M-rupture area, M-aspect ratio, and hypocenter locations in the down-dip and along-strike directions are developed.
Poster:
POSTER_SSA_20180517_NGA-Sub_Source_parameters_Chilean_earthquakes
Abstract: Two-dimensional (2D) spatial attenuation maps are produced for the crust of western Tibet using local earthquakes which are recorded by an array of 30 broadband stations operated from July 2007 to May 2011. Initially estimation of coda waves attenuation (Qc-1 ) is done using single isotropic model and subsequently relative contribution of scattering (Qsc-1 ) and intrinsic (Qi-1) attenuation have been calculated using Multiple Lapse Time Window Analysis (MLTWA) under the assumption of uniform distribution of multiple isotropic scattering effects for the frequency bands of 1-2, 2-4, 4-8, 8-16 and 12-24 Hz, respectively. All the events are selected on the basis of high signal to noise ratio having hypocentral distance within 200 km from the respective stations. The obtained Q values show a strong frequency dependent nature which can be correlated to the degree of tectonic complexity and the heterogeneities present in the medium. As a whole, the intrinsic absorption is found to be the dominant mechanism at all the frequencies which is quite consistent with the geo-tectonic complexity in the region. The obtained values of Q are in good agreement with other segments of Himalaya and Tibet as well as different tectonic regions in the world. Keywords: MLTWA, Intrinsic, scattering, coda wave, western Tibet
Poster:
Rahul Biswas
Abstract: With the exception of isolated and largely near-shore deployments of ocean-bottom seismometers (OBSs), most seismic instrumentation is located on land, although two-thirds of Earth’s surface is covered with oceans. Large earthquakes are generally confined to subduction zones or other plate boundaries, leading to an uneven distribution of seismic sources. This heterogeneity, coupled with the land-based limitations for most for the Earth’s interior, leads to significant unsampled parts of the Earth. Our work is motivated by the planning of a Joint Task Force to develop concepts and applications for Science Monitoring and Reliable Telecommunication (SMART) cables. Over a million kilometers of submarine telecommunication cables currently exist, which are unavailable to the scientific community for acquisition of geophysical data. If these cables are gradually replaced by SMART cables with oceanographic and seismic sensors at roughly 75 km intervals, one significant benefit to our science will be the near-ubiquitous extent of seismic receivers across the oceans, affording an unprecedented opportunity for both monitoring and modeling. In previous work we presented ray tracing through a 1D reference model to predict improvements to ray coverage afforded by sensors on SMART cables, compared to existing land-based seismic network coverage. Here we extend that modeling, tracing P and S rays through the SALSA3D global tomographic model. We compare results of this exercise to those for the iasp91 model with, and without, the SMART cable sensors.
Poster:
SSA_2018_poster_Rowe_final
Abstract: The study of the crust using receiver functions can provide valuable geological information, such as average crustal composition, its formation dynamics and the tectonic evolution of a region, as well as serve as an initial reference for the generation of seismic wave velocity models to improve earthquake location. To fill in gaps in information on the crust of the Amazonian Craton and adjacent provinces in Brazil, we used receiver functions and H-k stacking to estimate crustal thicknesses and the Vp/Vs ratios. The results indicate that the crust of the study region is predominantly felsic, with an average Vp/Vs around 1.73 and an average thickness of 38.2 km, with a range of 27.4-48.6 km. Minimum curvature interpolation of the crustal thickness values has made it possible to delimitate of the Amazonian Craton, which corresponds to the area with an average thickness equal to or greater than 39 km. In addition, it was possible to identify its potential cratonic blocks, as well as the Paranapanema Block of Paraná Basin. The geometry of the craton, defined by its crustal thickness, is corroborated by the distribution of natural seismicity that accompanies its edges. These are related to suture zones between the Amazonian, São Francisco/Congo and Paranapanema paleocontinents. The sedimentary basins that have undergone rifting processes have a thinner crust, usually less than 37 km thick. Due to the great variability of the results, it was not possible to determine a characteristic value of crustal thickness or Vp/Vs ratio for each structural province located in the study region.
Poster:
Poster_final_version
Abstract: The seismic deformation in the Andean retro arc zone is characterized by having compressive earthquakes at superficial and intermediate dephts. Examples of these are; the earthquakes of September 13, 1962 in Talavera del Esteco, Salta with a magnitude of 7,0 associated to a maximun intensity of IX in the Modified Mercalli Scale (IMM); the earthquakes of September 23, 1887 in the boundary between Argentina and Bolivia in the province of Salta with a maximun intensity in the Modified Mercalli Scale (IMM) of IX (INPRES, 2017) and the earthquake of January 16, 1944 in San Juan with an M=7,0 (Alvarado and Beck, 2006) . The aim of this job is to obtain a seismotectonic analysis of Jujuy earthquake on 6 October 2011, at 11:12 local time (14:12 UTC), with epicenter at about 100 km east of San Salvador de Jujuy city. This research includes an accurate determinaton of its location parameters, focal mechanism and the aftershock sequence to have a better knowledge of the seismogenic source of this seismic event. The relocation of the hypocenters was carried out with software hypoDD (Walhauser, 2002) and the velocity model used in this process is the used for INPRES (Sánchez et al., 2013). The results obtained show improvements in the definition about the rupture zone due to the aftershock propagation and detection of active secundary seismic sources associated to the main fault. The results are compared with previous studies to understand the seismic surface deformation in the transition zone between thin-skinned deformation observed in the Bolivian Andes and the Basement deformation observed in Sierras Pampeanas (Jordan et al., 1983).
Poster:
Póster Luciana Lopez
Abstract: Seismic risk is a crucial issue for South Caucasus, which is the main gateway between Asia and Europe. The goal of this work is to propose new methods and criteria for defining an overall approach aimed at assessing and mitigating seismic risk in Georgia. Seismic hazard assessment means the identification of zones of similar levels of earthquake hazard expressed with ground motion parameters ( acceleration, velocity, displacement, Intensity) . This abstract presents the results of preliminary study of seismic microzonation of the city of Gori (Georgia) that was done in the frame of CNR (National Research Council of Italy) project – Preliminary study for the assessment of seismic risk in strategic cities of “Georgia”. The city of Gori is the central of Shida Kartli region (Mkhare) and is located on both sides of Liachvi and Mtkvari rivers, in the 135 km2 around the Gori fortress. The seismic microzonation map of level 1 of Gori was carried out in the light of 1) already available data (i.e., topographic map and boreholes data), 2) results of new geological surveys and iii) geophysical measurements (i.e., MASW and noise measurements processed with HVSR technique). So we have done seismic free field investigations full of the city and over the most strategic buildings and important parts of Gori : the city hall, the hospital, the Rugby stadium, Castel of Gori and museums and central square. Our preliminary results highlights the presence of both stable zones susceptible to local amplifications and unstable zones susceptible to geological instability. Our results are directed to establish the set of actions aimed at risk mitigation before the initial onset of the emergency, and to the management of emergency once the seismic event has occurred. The products obtained will constitute the basic elements of an integrated system aimed at reducing the risk and improving the overall safety of people and infrastructure in Georgia.
Poster:
SSA_2018_Poster_Zura gogoladze
