DETERMINATION OF THE SOURCE MECHANISM AS WELL AS MATERIAL ANALYSIS OF INTERMEDIATE AND DEEP EARTHQUAKES IN THE SUMATRA SUBDUCTION ZONE IN 1970-2018 PERIOD

• Main Author: JUANGGA SIREGAR NIM: 12314069, HARI
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/27729
• Institution: Institut Teknologi Bandung

<p align="justify">From 1970 to 2018, there were at least five intermediate and deep earthquakes occurring on the Sumatra with magnitude moment greater than 5.5 and depths of more than 150 km under seismic gap. Determination of the focal mechanism of the five earthquakes is conducted to estimate the dominant forces acting around the earthquake event, whether the negative buoyancy of the subduction plate or the frictional force of the mantle and its constituent material. The earthquakes were recorded with a minimum of four stations three components by Meteorological, Climatological, and Geophysical Agency (BMKG) and Incorporated Research Institutions for Seismology (IRIS). Identification of focal mechanism was done by moment tensor inversion by using ISOLA-GUI where the waveforms were filtered using band pass filter with frequency range 0.01-0.03 Hz. From the data processing, the beach ball map will be obtained as a representation of dominant forces around the earthquake, as well as to approximate the surrounding material. From north to south Sumatra, the interpretation of the cause of the earthquake varies. The negative buoyancy force became the dominant force for two earthquakes around the north of Sumatra Island dan olivine in peridotite had not experienced phase changes. An intermediate earthquake that has a normal fault mechanism (down dip compression) can be caused by the occurrence of melting on spinel lherzolite, which is a subducting plate which subdued because it enters the mantle area which exceeds 10000C which causes the negative buoyance force to decrease and produce a normal fault. From the source mechanism in the form of down dip compression for two deep earthquake events that occur around the south of Sumatra Island, it can be interpreted that the frictional force of the mantle dominates causing a sudden slip. The hypothesis used in connection with the occurrence of down dip compression for deep earthquakes is the metastability hypothesis where an earthquake occurs due to transformational faulting in the metastable zone of the peridotite mantle.<p align="justify">