Simeulue Earthquake in 2008

Crustal Deformation Observed by Synthetic Aperture Radar (SAR)

Released: Feb. 25, 2008, Japanese version of this page

Crustal Deformation by InSAR

Interferogram[PNG: 514KB]
  1. An earthquake with a magnitude 7.4 occurred at Simeulue, Indonesia on February 20, 2008 as the result of thrust faulting on the boundary between the Australia and Sunda plates.
  2. We generated a SAR interferogram, which shows crustal deformation due to the earthquake, from ALOS PALSAR data acquired on October 3, 2006 and February 21, 2008.
  3. The maximum Line-of-sight (LOS) displacement toward the satellite amounted to around 59 cm. Unit vector to the satellite (e, n, u) = (-0.730, -0.153, 0.666).
  4. We estimated a rectangular fault model with a uniform slip based on the SAR interferogram. The estimated fault with a length of around 45 km slipped by around 2.6 m parallel to the NW-SE trending Sunda trench .
  5. This earthquake is located between the 2004 and 2005 megathrust earthquakes. We reported that there exists a seismic gap around 50km in length between the 2004 and 2005 earthquakes at the annual fall meeting of the Seismological Society of Japan in October 2005. The 2008 earthquake with a moment magnitude of 7.4 and around 45 km length covered this seismic gap. Consequently, seismogenic zone 1,670km in length parallel to the Sunda trench released seismic energy without leaving seismic gap.
  6. Mw8.4. earthquake occurred off the southern part of Sumatra Island on September 12, 2007.
  7. Mega and large thrust earthquakes occurred for only a five-year period from 2004 and 2008 covering most part of a large area around 2,300 km in length parallel to the Sunda trench .
  8. There exists a seismic gap about 370 km in length off Padang. An earthquake with a magnitude of over 8.5 occurred in this area in 1797.
  9. This research showed that the SAR interferogram is very effective to locate the earthquake fault and its slippage.

Earthquake Fault Model

Preliminary rectangular fault model with uniform slip
We estimated fault parameters with constraints on strike, dip , rake from Harvard CMT Solution.

Fault model

Estimated fault parameters are as follows:
2.519N, 96.130E, D=18.4km, L=44.8km, W=50.6km, Strike=302, Dip=4, Rake=96, Slip 2.64m, Mw=7.52 (Rigidity=40GPa)

Earthquakes along Sunda Trench

seismic gap

Satellite and Sensor

PALSAR sensor onboard "Daichi" (ALOS) satellite launched by Japan Aerospace Exploration Agency on January 24, 2006

Simeulue Earthquake in 2008

Date-time February 20, 2008 15:08 (Local time), 17:08 (JST), 8:08 (UTC)
Hypocenter location 2.778°N, 95.978°E Depth:35 km (USGS)
Magnitude 7.4 (USGS)