Ⓔ Kinematic and Dynamic Inversion of the 2008 Northern Iwate Earthquake by S. Ruiz * and R. Madariaga Abstract We perform kinematic and dynamic inversion of the 24 July 2008 (M w 6.8) Northern Iwate intermediate depth earthquake in Japan using strong-motion records from the K-NET and KiK-net networks. The rupture of this moderate mag- nitude earthquake is modeled as a simple elliptical patch. The optimal solutions are found comparing observed and synthetic records using an L 2 norm and the neighbor- hood algorithm to search for the best solution, followed by an exploration of solution space with a Monte Carlo technique. The geometry of the rupture, rupture velocity, and slip distribution are estimated by kinematic inversion. The rupture geometry, stress, and friction parameters are obtained by dynamic inversion. Both approaches converge to very similar source models with semiminor axes of 4 km, maximum slip of about 4 m, and large stress drops in the 30–45 MPa range. Rupture duration was less than 3 s because of very high sub-Rayleigh rupture propagation speeds. Energy release rate for the best models was in the range 23–36 MJ=m 2 , a rather large value for events of this size. For both kinematic and dynamic inversion we found families of solutions that fit the strong-motion data within a certain error, confirming the strong trade-off among inverted parameters. Finally, we demonstrate that dynamic inversion solutions are controlled by the dynamic similarity parameter κ and by seismic moment M 0 . These two parameters define a region of model space where dynamically similar models fit the observations with approximately the same misfit. Online Material: Figures that compare observed and synthetic waveforms for all available stations and comparison of Fourier spectrum of observed and synthetic seis- mograms. Introduction The Iwate 2008 intraslab intermediate depth (M w 6.8) earthquake occurred inside the subducted Pacific plate in northern Japan (Japan Meteorological Agency [JMA], Suzuki et al., 2009). The epicenter of the earthquake was located on land so that it had an excellent azimuthal coverage by strong- motion instruments of the K-NET and KiK-net networks. The maximum JMA seismic intensity was 6− and PGA val- ues larger than 1g were observed at a few sites. Strong in- termediate earthquakes of this kind occur often in Japan, for instance the 1987 M JMA 6.7 eastern Chiba event (Fukuyama, 1991); the 1993 M w 7.6 Kushiro-oki event (Ide and Takeo, 1996); the 1994 M w 8.2 Hokkaido Toho-oki (Shikotan) earth- quake (Kikuchi and Kanamori, 1995); the 2001 M w 6.7 Geiyo earthquake (Miyatake et al., 2004); or the 2003 M 7.1 Miyagi- oki earthquake (Okada and Hasegawa, 2003). Thanks to the dense seismic and strong-motion networks of Japan it is pos- sible to study these events in detail because local site effects are limited for the stations located closer to the epicenter. The conventional approach to invert seismic ruptures in the near field is to do a kinematic inversion of the observed records in order to compute the distribution of slip or slip rate on the fault for simple models of the rupture process. From these kinematic models of the rupture process it is then pos- sible to compute dynamic source parameters (Fukuyama and Mikumo, 1993; Ide and Takeo, 1996; Bouchon et al., 1998; among others). Many approximations used in the kinematic models affect the determination of the dynamic parameters (Guatteri and Spudich, 2000; Piatanesi et al., 2004), propa- gating errors from the kinematic inversion to the dynamic simulation. A better method would be to invert directly for stress and strength distribution using fully dynamic models. Dynamic inversion is difficult because we need exceptionally well-recorded events with limited site effects. Dynamic in- version is also expensive because at each step in the inversion *Also at Laboratoire de Géologie, Centre National de la Recherche Sci- entifique, École Normale Supérieure, 24 Rue Lhomond, 75231 Paris Cedex 05, France. 694 Bulletin of the Seismological Society of America, Vol. 103, No. 2A, pp. 694–708, April 2013, doi: 10.1785/0120120056