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A research of tsunami generated by the October 25th 2010 earthquake at Mentawai Western of Sumatra has been investigated. The observation of tsunami run up is about 5.7-7.4 m at three locations in the South and North Pagai. Numerical simulation of tsunami using the source mechanism obtained from BMKG results 3.8 m of tsunami wave height, while the propagation model shows that tsunami reach Enggano and Padang for about 38 and 58 minutes close to the tsunami travel time observation. It is clearly showed that the result of run up model is lower than its observation. From the calculation of the magnitude, it is obtained that the tsunami magnitude is about 8.1. This value is higher than the moment magnitude which is only 7.4. It can be conclude that the tsunami Mentawai can be characterized as an abnormal tsunami. This tsunami can also be categorized as a Tsunami Earthquake (TsE).

Introduction
Many studies of some great earthquakes in subduction zone of Sumatera had been carried out. Those investigations have contributed significantly on the seismic hazard potential at this area. Natawidjaja, 2007 noted that the potential megathrust earthquake at the area of the subduction depends on the fault segmentation, the dimension of the locked region and the history of the earthquake. These parameters determine the strain energy accumulation area that can generate a big earthquake. Subarya et al, 2006 had been investigated the great earthquake of Aceh-Andaman (2004, Mw 9.15), while Briggs et al, 2006, investigated the Nias Simelue (2005, Mw 8.7). Both of the earthquakes were characterized by the seismic gap zone. The Aceh Earthquake was already signed by the Simeuleu Earthquake of 2002 (Mw7.4), and then the Aceh Earthquake was assumed as an earthquake-triggered of the Nias Earthquake which occurred three months later after that.

After a series of two large earthquakes in the northern zone of Sumatra, Natawidjaja et al, 2007 predicted the megathrust of Mentawai Earthquake in the south of Sumatera. This prediction based on a study of paleogeodesy and paleoseismic (Natawidjaja, 2003) that noted the last major earthquake in Mentawai had occurred in the 1300’s and 1600’s, therefore, the cycle of the Mentawai Megathrust Earthquake is about 200 years.

Most of the big earthquakes occurred at the Sumatera area generated a tsunami. Jaiswal et al., (2006), noted that there were 33 tsunamis occurred at the Sumatera area. As a part of Sunda Arc, Sumatera had been much more active than Java. Table 1 gives a list of Tsunami Occurrence in Sumatera area.

From the list of tsunami events, generally, the tsunamis in the Sumatera area are generated by an earthquake with a magnitude of more than 7 Ms. The Mentawai Earthquake which happened on Oktober 25th, 2010 is an earthquake that generated a tsunami due to its magnitude and depth. This study investigated a Mentawai Tsunami which generated by an earthquake with a magnitude of 7.2 Mw. The earthquake has occurred along the plate interface boundary between the Australia and Sunda plates at Pagai Selatan Sumatera. According to BMKG, the earthquake located at the location of 3.6oS and 99.9oE with 10 km depth. This big earthquake occurred due to the movement of the Australia Plate with respect to the Sunda Plate with a velocity of approximately 50-70 mm/yr.

The Mamoru Nakamura’s Program was applied in this study to run a modeling of the Mentawai tsunami. A field study to the Mentawai Islands after the event had also been carried out in this research to provide the height of tsunami run-up in that area to validate the tsunami modeling