We have undertaken the first paleoseismological study on an upper plate fault in Chile. The selected structure was the Mejillones Fault, which is marked by a conspicuous fault-scarp. Using cosmogenic ...10Be and OSL dating and detailed sedimentary logging of trenches, we have constrained the abandonment of two alluvial surfaces by fault activity at ca. 35 ka and ca.14 ka. Based on stratigraphic observation we characterized the fault evolution in four intervals over the last ca. 35 ka. During the first three intervals the fault had a steady slip rate of 0.61 ± 0.26 m/ka. The fourth interval is delineated by the last vertical fault slip and the accumulation of un-deformed hillslope deposits after ca. 3.3 ka and has a slip rate of 0.22 ± 0.06 m/ka. The younger surface abandonment was caused by two Mw 7 paleoearthquakes with a recurrence interval of 5.0 ± 3.5 ka. The third interval is characterized by the interaction of hillslope deposits and aseismic slip and/or centimeter scale seismic slip events. At ca. 3.5 ka, a last large (Mw 6.6) earthquake took place. The recurrence intervals of large (Mw > 8.5) subduction earthquakes do not appear to be the same as the recurrence intervals of the Mw 7 events on the upper plate Mejillones Fault.
La descripción de la dinámica de penetración de intrusos en medios granulares no sólo es relevante para la Física sino también para procesos geofísicos y ramas de la industria, en particular la ...construcción en zonas de terremotos. En el presente trabajo utilizamos la técnica de Acelerometría Lock-in para estudiar la penetración de intrusos pasivos en un medio granular cuasi-bidimensional fluidizado mediante agitación lateral. Esta técnica demuestra que existen dos dinámicas de penetración bien definidas en la medida que el intruso se hunde en el medio granular. Understanding the penetration dynamics of intruders in granular beds is relevant not only for fundamental physics, but also for geophysical processes and construction on sediments or granular soils in áreas potentially affected by earthquakes. In this work, we use Lock-in accelerometry to study the penetration of passive intruders into quasi-2D granular matter fluidized by lateral shaking. We observed that there are two well-defined stages in the penetration dynamics as the intruder sinks into the granular material. PACS: 45.70.-n, 45.70.Mg, 07.07.Df, 07.50.Qx
The Korean Peninsula is located in the far-eastern Eurasian plate margin where crustal structures vary laterally, causing significant raypath-dependent modulations of crustal phases. The ...discriminative variations of crustal phases hinder application of conventional local magnitude scales in the continental margin. The mantle-lid phase is less affected by the crustal structures than the crustal phases, providing a better constraint to magnitude estimation. A regional body-wave magnitude scale based on the mantle-lid P wave (Pn), m ^sub b^(Pn), is developed for regional events around the Korean Peninsula. The m ^sub b^(Pn) scale is determined to be m ^sub b^(Pn) = 0.380 (±0.299) + log A + 2.012 (±0.122) log d, where A is the peak-to-peak Pn amplitude in μm and d is the epicentral distance in km. The m ^sub b^(Pn) estimates of regional events around the Korean Peninsula are determined. The m ^sub b^(Pn) estimates are compared with other available magnitude estimates (m ^sub b^(Lg), M ^sub L^). The influence of structures beneath stations on Pn amplification is investigated from inter-station magnitude residuals. A characteristic spatial variation of inter-station magnitude residuals with strengths mostly between -6 and 6 %, but with maximum strengths of ±10 %, is observed. The inter-station magnitude residuals appears to be correlated well with geological and seismic structures in the crust.PUBLICATION ABSTRACT
Rapid magnitude estimate procedures represent a crucial part of proposed earthquake early warning systems. Most of these estimates are focused on the first part of the P-wave train, the earlier and ...less destructive part of the ground motion that follows an earthquake. Allen and Kanamori (Science 300:786-789, 2003 ) proposed to use the predominant period of the P-wave to determine the magnitude of a large earthquake at local distance and Olivieri et al. (Bull Seismol Soc Am 185:74-81, 2008 ) calibrated a specific relation for the Italian region. The Mw 6.3 earthquake hit Central Italy on April 6, 2009 and the largest aftershocks provide a useful dataset to validate the proposed relation and discuss the risks connected to the extrapolation of magnitude relations with a poor dataset of large earthquake waveforms. A large discrepancy between local magnitude (ML) estimated by means of tau^sub p^^sup max^ evaluation and standard ML (6.8 ± 1.5 vs. 5.9 ± 0.4) suggests using caution when ML vs. tau^sub p^^sup max^ calibrations do not include a relevant dataset of large earthquakes. Effects from large residuals could be mitigated or removed introducing selection rules on tau^sub p^ function, by regionalizing the ML vs. tau^sub p^^sup max^ function in the presence of significant tectonic or geological heterogeneity, and using probabilistic and evolutionary methods.PUBLICATION ABSTRACT
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