FAULT INSTABILITY AND STATIC COULOMB FAILURE STRESS OF M6,5 PIDIE JAYA, ACEH 2016 EARTHQUAKE

• Main Author: KUSUMAWATI (NIM: 22415301), DIAN
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/26619
• Institution: Institut Teknologi Bandung

The M6,5 Pidie Jaya strike slip earthquake shook up Pidie Jaya, Aceh, on <br /> <br /> Wednesday 7th of December 2016. The aftershocks lasted until January 2017. The <br /> <br /> aftershocks which were recorded by BMKG station on 7-19 December 2016, <br /> <br /> depict northwest – southeast cluster orientation. Meanwhile, the aftershocks <br /> <br /> which were recorded by Aceh Aftershock Station on 14 December 2016-15 <br /> <br /> January 2017, depict different cluster orientation, that is northeast-southwest. <br /> <br /> These perpendicular clusters orientation may complicate the interpretation of <br /> <br /> focal mechanism fault plane. The interpretation of fault plane itself is important <br /> <br /> for the input of seismic hazard map. Fault instability and static Coulomb failure <br /> <br /> stress (&#916;CFS) concept were applied in this research in order to interpret fault <br /> <br /> plane orientation of M6,5 Pidie Jaya focal mechanism and explain the twoperpendicular- <br /> <br /> cluster, BMKG catalog and AAS catalog, phenomenon. Aftershock <br /> <br /> prone area is also analyzed from the result. Taguchi Orthogonal array method <br /> <br /> was applied to grasp &#916;CFS parameter responses and to test the &#916;CFS parameter <br /> <br /> sensitivity. <br /> <br /> The fault instability analysis showed that northeast-southwest fault orientation is <br /> <br /> more unstable in Sumatra regional stress tectonic condition. This orientation was <br /> <br /> used as reference orientation for fault plane model of Pidie Jaya &#916;CFS. From the <br /> <br /> sensitivity test using Taguchi Orthogonal array it was found that the dip has the <br /> <br /> highest effect to &#916;CFS modeling for the applied scenario. Therefore, the dip’s <br /> <br /> orientation for Pidie Jaya &#916;CFS modeling was estimated from AAS aftershocks <br /> <br /> distribution. The stress distributions from Pidie Jaya &#916;CFS modeling explain the <br /> <br /> two-perpendicular-aftershock cluster phenomenon. Positive &#916;CFS was found on <br /> <br /> shallow depth (1-7 km) oriented northwest – southeast, perpendicular to the fault <br /> <br /> plane model orientation. This stress was interpreted as the cause of BMKG <br /> <br /> aftershocks cluster orientation, and responsible for the shallow depth-fracture <br /> <br /> zone (oriented northwest – southeast) features. Those fracture zone features were <br /> <br /> formed although the orientation is not in the optimum direction to fail (based on <br /> <br /> Instability concept), due to stress redistribution of positive &#916;CFS on the shallow <br /> <br /> depth. The AAS aftershocks cluster has good correlation with the positive &#916;CFS <br /> <br /> which lies on the model fault plane within depth of 16-28 km. Moreover, &#916;CFS <br /> <br /> stress distribution on shallow depth (1-7 km) also explained relatively lack of <br /> <br /> iv <br /> <br /> events in the southeast mainshock, that is in the vicinity of Samalanga-sipopok <br /> <br /> Fault area.