Coseismic slip distribution for the M_w 9 2011 Tohoku‐Oki earthquake derived from 3‐D FE modeling

Abstract

[1] The coseismic slip distribution of the M w 9.0 2011 Tohoku-Oki earthquake has been estimated by inverting near-field onshore and offshore geodetic data, using Green's function calculated with a 3-D finite element (FE) model. The FE model simulates several geophysical features of the subduction zone that hosted the rupture surface of the event. These features include a 3-D geometric configuration and distribution of material properties of the tectonic system, a precise geometric configuration of the irregular rupture surface, and an irregular free surface according to the topography and bathymetry. A model that simulates rupture along the interface between the relatively weak overriding Okhotsk plate and stiff subducting slab of the Pacific Plate requires less slip to produce the observed surface deformation, compared to a model having uniform material properties across the rupture interface. Furthermore, the estimated slip of the heterogeneous model is more widely distributed over the shallow portion of the plate boundary, whereas the estimated slip of the homogeneous model is more focused updip of the epicenter. This demonstrates the sensitivity of inverse analyses of geodetic data for the 2011 Tohoku-Oki earthquake to the simulated domain geometry and configuration of material properties.

Coseismic deformation due to the 2011 Tohoku-oki earthquake: influence of 3-D elastic structure around Japan

“…Seismic moment and potency in each structure are slightly smaller than those obtained in the combined inversion. These decreases are consistent with the findings of Diao et al (2012) and Kyriakopoulos et al (2013).…”

“…Instead, fitting in the onshore region also plays an important role. This result conflicts with Kyriakopoulos et al (2013), who emphasized its importance. One of the reasons for this mismatch might stem from the elastic contrast used.…”

“…One of the reasons for this mismatch might stem from the elastic contrast used. The rigidity ratio in our SLAB model is 2.4, while Kyriakopoulos et al 's (2013) model used 3.7. According to studies of seismic tomography (e.g., Nakajima et al 2001;Huang et al 2011), velocity anomalies (V P and V S ) in the slab compared to the surrounding mantle are ~6 %, implying that even our contrast might be on the high end.…”

“…According to studies of seismic tomography (e.g., Nakajima et al 2001;Huang et al 2011), velocity anomalies (V P and V S ) in the slab compared to the surrounding mantle are ~6 %, implying that even our contrast might be on the high end. Kyriakopoulos et al 's (2013) larger contrast may lead to an overestimate of the effect of elastic heterogeneity. Their elastic contrast also leads to poor fit of the vertical displacements ( Fig.…”

“…Conversely, the consideration of a strong slab (a slab with increased rigidity) in the coseismic inversion was shown to lead to a decrease in inferred seismic moment compared to a homogeneous model (Hsu et al 2011;Kyriakopoulos et al 2013). Consideration of surface topography and lateral heterogeneity from seismic tomography was also found to lead to a better fit to the observed coseismic surface displacements (Pulvirenti et al 2014;Romano et al 2014).…”