Examinando por Autor "Meng, Xiaofeng"

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Detailed spatiotemporal evolution of microseismicity and repeating earthquakes following the 2012 Mw 7.6 Nicoya earthquake
(Universidad Nacional, Costa Rica., 2017) Yao, Dongdong; Walter, Jacob; Meng, Xiaofeng; Hobbs, Tiegan; Peng, Zhigang; Newman, Andrew V.; Schwartz, Susan Y.; Protti, Marino
We apply a waveform matching technique to obtain a detailed earthquake catalog around therupture zone of the 5 September 2012 moment magnitude 7.6 Nicoya earthquake, with emphasis on itsaftershock sequence. Starting from a preliminary catalog, we relocate ~7900 events using TomoDD to betterquantify their spatiotemporal behavior. Relocated aftershocks are mostly clustered in two groups. Thefirst isimmediately above the major coseismic slip patch, partially overlapping with shallow afterslip. The secondone is 50 km SE to the main shock nucleation point and near the terminus of coseismic rupture, in a zone thatexhibited little resolvable afterslip. Using the relocated events as templates, we scan through the continuousrecording from 29 June 2012 to 30 December 2012, detecting approximately 17 times more than templateevents. Wefind 190 aftershocks in thefirst half hour following the main shock, mostly along the plateinterface. Later events become more scattered in location, showing moderate expansion in both along-trench and downdip directions. From the detected catalog we identify 53 repeating aftershock clusters withmean cross-correlation values larger than 0.9, and indistinguishably intracluster event locations, suggestingslip on the same fault patch. Most repeating clusters occurred within thefirst major aftershock group. Veryfew repeating clusters were found in the aftershock grouping along the southern edge of the Peninsula,which is not associated with substantial afterslip. Our observations suggest that loading from nearby afterslipalong the plate interface drives spatiotemporal evolution of aftershocks just above the main shock rupturepatch, while aftershocks in the SE group are to the SE of the observed updip afterslip and poorly constrained.
Far-field triggering of foreshocks near the nucleation zone of the 5 September 2012 (MW 7.6) Nicoya Peninsula, Costa Rica earthquak
(Elsevier, 2015-12-01) Walter, Jacob; Meng, Xiaofeng; Peng, Zhigang; Schwartz, Susan; Newman, Andrew; Protti, Marino
On 5 September 2012, a moment magnitude (MW) 7.6 earthquake occurred directly beneath the Nicoya Peninsula, an area with dense seismic and geodetic network coverage. The mainshock ruptured a portion of a previously identified locked patch that was recognized due to a decade-long effort to delineate the megathrust seismic and aseismic processes in this area. Here we conduct a comprehensive study of the seismicity prior to this event utilizing a matched-filter analysis that allows us to decrease the magnitude of catalog completeness by 1 unit. We observe a statistically significant increase in seismicity rate below the Nicoya Peninsula following the 27 August 2012 (MW 7.3) El Salvador earthquake (about 450 km to the northwest and 9 days prior to the Nicoya earthquake). Additionally, we identify a cluster of small-magnitude (<2.2) earthquakes preceding the mainshock by about 35 min and within 15 km of its hypocenter. The immediate foreshock sequence occurred in the same area as those earthquakes triggered shortly after the El Salvador event; though it is not clear whether the effect of triggering from the El Salvador event persisted until the foreshock sequence given the uncertainties in seismicity rates from a relatively small number of earthquakes. If megathrust earthquakes at such distances can induce significant increases in seismicity during the days before another larger event, this sequence strengthens the need for real-time seismicity monitoring for large earthquake forecasting.