Revisiting the 1995 Kobe earthquake in Japan: preliminary results of image correlation using pre- and post-events aerial photos

Abstract:

Fault geometry and slip distribution of surface ruptures associated with earthquakes plays a key role in understanding seismic rupture behaviors. Over the past decades there has been technological advances in sub-pixel correlation of pre- and post-earthquake images, and this provides an opportunity to map in detail the earthquake surface ruptures. Here we introduce preliminary results of mapping the surface rupture associated with the Jan. 17, 1995 Mw 6.9 Kobe, Japan, earthquake using pre- and post-events aerial images. We note that the earthquake was an inland shallow (~17 km) event, and the surface rupture occurred only on Awaji Island (to the southwest of the epicenter). The surface rupture has mapped mainly by field investigations immediately after the event, and their results indicate that the surface rupture was about 10.5 km in length mainly along the Nojima fault with 1 to 2.5 m of dextral dominant offset. For the area, we use a pair of aerial images acquired on Apr. 21, 1991 (pixel size of 0.5 m) and Jan. 20, 1995 (pixel size of 0.2 m), by GSI in Japan, to measure horizontal displacement field during the earthquake. Aerial images were processed by the MicMac, developed by IGN in France. Our preliminary results show that trace of surface ruptures corresponds to the previously mapped rupture trace and offset-variations along the fault is continuously observable. Offset-variations in N-S and E-W trending displacement fields are interrelated mostly at where the rupture geometry is relatively complex.