Artículos científicos
URI permanente para esta colecciónhttp://10.0.96.45:4000/handle/11056/17882
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Ítem Crustal Velocity Anomalies in Costa Rica from Ambient Noise Tomography(Springer Nature, 2019-08-24) Nuñez Alpízar, Evelyn; Schimmel, M.; Stich, D.; Iglesias, A.We derive group velocity maps for crustal Rayleigh waves across Costa Rica and corresponding 3-D shear-wave velocity structure from ambient noise cross-correlations between 56 seismic broadband stations. The daily inter-station cross-correlations for the period 2010–2015 of 56 seismic broadband stations are stacked and analysed to warrant a robust extraction of empirical Green’s functions which then are used to measure fundamental mode Rayleigh wave group velocities. Rayleigh wave dispersion curves show consistent patterns within the different geological domains in Costa Rica. Dispersion curves were evaluated in the microseism band from 5- to 17-s period and inverted for group velocity maps using iterative nonlinear travel time tomography. The group velocities at each grid point were inverted for 1-D profiles using a non-linear simulated annealing approach, and transformed into the 3-D velocity structure. The final tomographic model shows clearly the main velocity anomalies associated with tectonic and volcanic activity in Costa Rica. Three localized negative velocity anomalies are seen at all periods (5–17 s) consistent with deep-routed crustal-scale magmatic systems located beneath the Rincón de la Vieja-Miravalles, Arenal-Poás and Turrialba-Irazú volcanic systems, that showed activity over the last 100 years. High velocities can be found beneath the Talamanca arc in southeastern Costa Rica, where active volcanism stopped in the late Miocene. Significant along-strike variations in the morphology of the subducting Cocos plate are imaged consistently by velocity variations in the forearc.Ítem Yield estimate (230 kt) for a Mueller-Murphy model of the 3 september 2017, North Korean nuclear test (mbNEIC = 6.3) from teleseismic broadband P waves assuming extensive near-source damage(AGU Advancing Earth and Space Sciences, 2018) Chaves, Esteban; Lay, Thorne; Voytan, DimitriThe 3 September 2017 underground nuclear test (mbNEIC= 6.3) is the largest of six announced North Korean explosions. The event generated many P wave seismograms at global broadband seismic stations with good signal-to-noise ratio for periods less than ~5 s. Instrument deconvolution provides 435 stable broadband P wave ground displacement records in the period range 0.1 to 5.0 s. These are stacked in 26 azimuth/distance windows to average path and receiver effects. Waveform stacks and average amplitude of 4-Hz ground displacements are modeled assuming a Mueller-Murphy explosion source modelfor a granite source medium. Nonelastic pP delays consistent with burial depths in the mountainous source topography are considered, and explosion yield and an average constant-Q attenuation operator areestimated by fitting the waveforms. For a source depth of 750 m in heavily damaged environment, the estimated yield = 230 ± 50 kt andt*= 0.78 ± 0.03 s.