Geoscience Reference
In-Depth Information
the junction of the Eurasian, Australian, Pacific, and Philippine Sea Plates, resulting in
rugged topography, frequent earthquakes, and intensive volcanism (Indonesia, 2008).
The seismic manifestations of the region, bounded between latitudes 0-17
S and
longitudes 100-130°E, 5 days before and after the passing of satellite (orbits 215,
258), are shown in Figure 3a. Five events (EQ
4,5,21,33,37
) take place in the area and they
are with magnitude M 4.8 during the studied time period (see Table 1). On the back-
ground of the trend, to the north of the earthquake epicenter, we observe an increase
in the
E
z
component of about 8 mV/m, 26 hr before EQ
21
(Figure 3b). Figure 3b ill-
ustrates also the next increase in the
E
z
component of about 8 mV/m to the north of
EQ
5
and EQ
33
. It is highly probable that the disturbances in the
E
z
component are due
to the cumulative effect of occurred EQ
5
and forthcoming earthquake EQ33 (it is happ-
ened 107 hr later). The earthquake EQ37 of magnitude M 4.9 occurs on September 19,
1981 in the Sumatra region. The Sumatra region from the western part of Indonesia
is considered as a part of the Sunda arc, which results from the convergence between
the Indo-Australian and Eurasian Plates. As a product of the plate convergence, the
Sumatra region is considered to be one of the most seismically active regions in
Indonesia (Nanang and Gunawan, 2005).
°
Figure 3a.
Satellite orbits 215, 258, and positions of the earthquake epicenters for period of seismic
activity in August 12-September 1, 1981.
