- 1. Intoruction
-
On 14:55 September 2, 2009 (local time), an earthquake with magnitude
(Mw) 6.9 occurred in western Java, Indonesia. Our waveform analysis
shows that this earthquake occurred on a reverse fault, with a depth
of 50-60 km. This earthquake caused severe damage in western
Java. Many people were injured due to this earthquake. Many casualties
are also reported.
- 2. Location of this earthquake
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In this region, the Indo-Australia plate is subducting northward
beneath the Java island, which is located on the Eurasia plate
(Figs. 2-1, 2-2). Since the focal mechanism shows that the compression
axis is oriented in East-West, this event occurred in the subducting
plate, not on the plate boundary.
Fig. 2-1. Epicenter distribution obtained from USGS PDE (circles,
between 1973 and 2009). The source centroid location obtained by this
study is shown by the focal mechanism symbol.
Fig. 2-2. Vertical cross-section of the hypocenter distribution (USGS
PDE) along the profile A-B shown in Fig. 2-1. The star indicates the
source centroid location obtained by this study.
- 3. Rupture dutaion
-
Our inversion analysis shows that the fault rupture during this
earthquake took about 2-4 s (Fig. 3-1). This value is much smaller
than the typical duration for earthquakes of this magnitude (about 15
s for Mw=6.9 events, after Ekstrom and Engdahl, 1989, JGR).
Fig. 3-1. The estimated moment function. The blue line shows the
estimated moment function.
(Written by M. Nakano, Figures drawn by T. Yamashina)
Last update: September 3, 2009
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