Download Basin and Crustal Structure Model in Kinki Area and Long

International Workshop on Long-Period Ground Motion Simulation and Velocity Structures
Earthquake Research Institute, University of Tokyo, Tokyo, November 14-15, 2006
Basin and Crustal Structure Model in Kinki Area and
Long-Period Ground Motions
Tomotaka Iwata1*, Takao Kagawa2, Anatoly Petukhin2, & Yoshihiro Onishi2
1
Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan;;
Geo-Research Institute, Itachibori 4-3-2, nishi-ku, Osaka, 550-0012, Japan
*Author for correspondence, e-mail: [email protected]
2
Key words: basin model, crustal structure model, strong motion prediction
Abstract
We construct a prototype of basin and crustal structure model in Kinki area, SW of Japan, for strong ground
motion simulation of hypothetical crustal and subduction earthquakes. Using deep seismic exploration
experiments and three-dimensional tomography results, we construct the crustal velocity structure model in this
area. The basin structure models of Osaka, Kyoto, Nara, and Ohmi, by geophysical exploration surveys, are put
into this crustal structure model. To examine the applicability of the velocity structure model to long-period
ground motion simulation, waveform simulation of intermediate size event records is under conducting.
1. Introduction
Ground motion simulation and prediction based on
the source and the underground velocity structure
model are quite useful for understanding of strong
ground motion characteristics and related earthquake
disaster. For the sake of accomplishing reliable strong
motion simulations especially for subduction
earthquakes and inland crustal earthquakes, we start
to construct the sedimentary basin and crustal
velocity structure model in Kinki area by compiling
many seismic survey results and local basin models.
We show a prototype of the underground velocity
structure model and applicability of this velocity
model by simulating ground motion records for small
or intermediate size events observed dense strong
motion network (Iwata et al., 2006).
2. Construction of basin and crustal velocity
structure model
Figure 1 shows schematic cross section for crustal
velocity structure model with the subducting
Philippine sea slab in Kinki area. In 2004, deep
seismic exploration experiment crossing in Kinki area
was conducted by the project of regional
characterization of the crust in metropolitan areas for
prediction of strong ground motion (Ito et al., 2005).
Crustal structure and subducting slab structure were
studied by P-wave exploration surveys (e.g. Kodaira
et al,, Nakamura et al.,1998, 2002) and earthquake
records by the receiver function method (e.g.
Yamauchi et al, 2003) before this experiments. We
also referred seismic cross section database
(JAMSTEC, 2006; ERI, 2006). We also use the
velocity structure models for OBS (Ocean Bottom
Seismometer) measurements. Structural interfaces are
mainly obtained from P-waves and we give the
S-wave velocity value for each layer. In the
subducting area, the accression prism or the
sedimentary wedge are observed in the cross sections
of the exploration surveys. The thickness of this
sediment seems to be several kilometers and that
affects ground motion simulation from subduction
events (e.g. Yamada and Iwata, 2005).
In Kinki area, we have references for major
sedimentary basin models, e.g. Osaka, Kyoto, Nara,
and Ohmi (Shiga) basins. Especially, Osaka
sedimentary basin model is obtained by Kagawa et al.
(2004). We conducted additional microtremor H/V
measurements to construct Osaka-Kyoto-Nara
basin-border model and showed the contour map of
the seismic bedrock in Figure 2. The basement
interface of the sediment is explained by the spline
function (e.g. Koketsu and Higashi, 1992). In Figure
3, we show the NS cross section of the crustal and
basin structure along the Kii peninsula region.
Kii-Hanto-Nanto-Oki earthquake (MJ6.5), which
occurred near the source region of the hypothetical
Tonankai earthquake. Simulated ground motions will
be compared to the observed ones.
Acknowledgements
This study is supported by the ‘Regional
characterization of the crust in metropolitan areas for
prediction of strong ground motion’ project by MEXT,
Japan.
References
Figure 1. Schematic basin and crustal structure model.
Figure 2. Basement depth contour of the Osaka, Kyoto
and Nara basins.
Figure 3. NS cross section of the crustal model.
3. Estimation of applicability of the basin and
crustal structure model by waveform modeling
As we interpolate, extrapolate and average medium
parameters under assumption for constructing the
velocity structure model, this kind of velocity
structure model should be examined the applicability
of ground motion simulation. Here we performed
waveform modeling for the aftershock of the 2004
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