Abstract
We investigate the impact of source-side 3D velocity structure on teleseismic travel-time in back projection (BP) analysis of large earthquakes. We use travel-time data of teleseismic events recorded by the Hi-Net array to reveal how travel-time errors vary with source location. In a source area of a few hundred km, where travel-time error varies dominantly linearly, we propose a new interpolation scheme using earthquakes located around the mainshock rupture to calibrate the travel-time error, and validate it by relocating inland M > 5.0 earthquakes in central Japan. We then apply it to image the rupture of the 2002 Denali earthquake. The calibrated BP result shows that most of the high-frequency radiators are <15 km="" away="" from="" the="" surface="" rupture="" trace.="" the="" new="" result="" reveals="" that="" the="" rupture="" started="" on="" the="" susitna="" glacier="" fault="" with="" a="" speed="" of="" ∼1.4="" km/s,="" then="" propagated="" onto="" the="" denali="" fault="" and="" accelerated="" to="" a="" super-shear="" speed="" approaching="" the="" crustal="" p-wave="" velocity="" at="" approximately="" 30="" km.="" the="" location="" of="" super-shear="" transition="" and="" rupture="" speed="" in="" bp="" are="" highly="" consistent="" with="" that="" inferred="" from="" the="" timing="" and="" amplitude="" ratio="" of="" the="" super-shear="" and="" trailing="" rayleigh="" pulses="" observed="" on="" the="" near="" fault="" ps-10="" station.="" subsequently,="" the="" rupture="" stagnated="" for="" ∼15="" s="" before="" penetrating="" through="" the="" largest="" asperity,="" re-accelerated="" to="" a="" speed="" of="" ∼5.2="" km/s="" and="" continued="" on="" the="" last="" 60="" km="" of="" the="" denali="" fault="" and="" part="" of="" totschunda="" fault.="" this="" application="" shows="" the="" great="" potential="" of="" the="" new="" bp="" calibration="" strategy="" to="" refine="" the="" rupture="" imaging="" of="" other="">
Keywords
back projection, Denali earthquake, earthquake physics, strong motion, super-shear rupture, travel time calibration