Browsing by Author "Yamazaki, Fumio"
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Item Restricted Estimation of slip scenarios for megathrust earthquakes: a case study for Peru(University of California Santa Barbara, 2011-08-13) Pulido, Nelson; Tavera, Hernando; Perfettini, Hugo; Chlieh, Mohamed; Aguilar, Zenón; Aoi, Shin; Nakai, Shoichi; Yamazaki, FumioThe recent 2011 Tohoku-oki earthquake occurred in a region where giant megathrust earthquakes were not expected. This earthquake proved the difficulty to assess seismic hazard mainly based on information from historical earthquakes. In this study we propose a methodology to estimate the slip distribution of megathrust earthquakes based on a model of interseismic coupling (ISC) distribution in subduction margins as well as information of historical earthquakes, and apply the method to the Central Andes region in Peru. The slip model obtained from geodetic data represents the large scale features of asperities within the megathrust, which is appropriate for simulation of long period waves and tsunami modelling. For the simulation of a broadband strong ground motion it becomes necessary to introduce small scale complexities to the source slip to be able to simulate high frequency ground motions. To achieve this purpose we propose a “broadband” source model in which large scale features of the model are constructed from our geodetic scenario slip, and the small scale heterogeneities are obtained from a spatially correlated random slip model. The good agreement between the power spectral density (PSD) of our geodetic slip model, and the PSD of a slip model of the 2010 Maule earthquake, suggests that our methodology can be appropriate to typify megathrust earthquakes.Item Restricted Scenario source models and strong ground motion for future mega-earthquakes: application to Lima, Central Peru(Seismological Society of America, 2015-01) Pulido, Nelson; Aguilar, Zenón; Tavera, Hernando; Chlieh, Mohamed; Calderón, Diana; Sekiguchi, Toru; Nakai, Shoichi; Yamazaki, FumioThe 2011 moment magnitude (Mw) 9.0 Tohoku-Oki Japan earthquake occurred in a region where giant megathrust earthquakes were not expected. This earthquake proved the difficulty in assessing seismic hazard by relying mainly on information from historical and instrumental seismicity. To help improve the seismic-hazard assessment for such rare events, we propose a methodology to estimate the slip distribution of future megathrust earthquakes based on a model of interseismic coupling distribution in subduction margins, as well as information of historical earthquakes, and apply the method to the central Peru region, Lima. The slip model obtained from geodetic data represents the large scale features of asperities within the megathrust, which is appropriate for simulation of long-period waves and tsunami modeling. For the simulation of a broadband strong ground motion, we add small scale heterogeneities to the source slip to be able to simulate high frequencies. To achieve this purpose, we propose broadband source models constructed by adding short-wavelength slip distributions obtained from a Von Karman power spectral density function, to the slip model inferred from interseismic geodetic data. Using these slip models and assuming several hypocenter locations, we calculate a set of strong ground motions for Lima and incorporate site effects obtained from microtremors surveys and geotechnical data. Our simulated average pseudospectral accelerations (period 0.3 s) are above 1:5g for wide areas in Lima, which may be critical in terms of damage of low- to midrise masonry and reinforced concrete buildings, which characterize the majority of buildings in Lima.Item Restricted Strong motion simulation of the M8.0 August 15, 2007, Pisco earthquake; effect of a multi-frequency rupture process(Journal of Disaster Research, 2013-03) Pulido, Nelson; Tavera, Hernando; Aguilar, Zenon; Nakai, Shoichi; Yamazaki, FumioWe investigated the broadband frequency (0.05-30 Hz) radiation characteristics of the August 15, 2007, Mw8.0 Pisco, Peru, earthquake by simulating the near-source strong ground motion recordings in Parcona city (PCN) and Lima city (NNA). A source model of this earthquake obtained from long-period teleseismic waveforms and InSar data shows two separate asperities, which is consistent with the observation of two distinct episodes of strong shaking in strong motion recordings. We constructed a source model that reproduces near-source records at low frequency (0.05-0.8 Hz) as well as high frequency (0.8-30 Hz) bands. Our results show that the aforementioned teleseismic source model is appropriate for simulating near-source low frequency ground motion. Our modeling of the PCN record in the broad-frequency band indicates that a very strong high frequency radiation event likely occurred near the hypocenter, which generated a large acceleration peak within the first episode of strong shaking at PCN. Using this “broadband frequency” source model we simulated the strong ground motion at Pisco city and obtained accelerations as large as 700 cm/s2 and velocities as high as 90 cm/s, respectively, which may explain the heavy damage occurring in the city.