Electronic Theses and Dissertation

Patahan Sumatra merupakan sistem sesar menganan yang terbagi menjadi beberapa segmen.
Riwayat gempa bumi di Sumatra bagian utara mengindikasikan adanya patahan sekunder dan
segmentasi di utara maupun selatan Patahan Sumatra. Penelitian ini bertujuan mendeliniasi
Patahan Sumatra dan patahan sekunder di Sumatra bagian utara berdasarkan data gempa lokal.
Total 147 Dense Seismic Network telah dipasang di Sumatra bagian utara dimana 3693 gempa
lokal terekam sejak Desember 2019 – Juni 2020 yang ditentukan menggunakan HYPO71
berdasarkan rekaman gelombang P dan S. Gempa bumi kemudian direlokasi menggunakan
metode simultan relokasi gempa dan penentuan model kecepatan (VELEST) untuk
memperbaiki kualitas data menjadi lebih baik untuk 2463 gempa dengan azimuthal GAP
≤190o dan RMS < 0.5 s. Lokasi gempa kemudian diperbaiki lagi menggunakan metode
Double Difference sehingga mendapatkan pola distribusi yang tajam yang dapat memberi
gambaran liniasi patahan secara detail. Interpretasi detail liniasi dan orientasi patahan
dikombinasikan dengan data mekanisme fokal melalui metode polaritas gelombang pertama
(first polarity) dan model elevasi. Distribusi gempa menunjukkan bahwa Patahan Seulimeum
tersegmentasi di bagian utara, diberi nama Seulimeum-West dan Seulimeum-North yang
membentuk cekungan di Pulau Weh dan diidentifikasi sebagai sesar menganan (dextral strike
slip). Seulimeum-central terliniasi di sepanjang selatan Gunung Api Seulawah dengan pola
dextral strike-slip. Patahan Seulimeum juga menunjukkan adanya segmentasi di bagian selatan
yang dinamai Seulimeum-South yang memiliki pola sesar naik (thrust fault) dan pola sesar
menganan. Klaster di selatan Segmen Aceh diidentifikasi sebagai Segmen Jantho yang secara
umum memiliki pola sesar normal. Patahan Sumatra tersegmentasi di bagian selatan Segmen
Aceh dan diberi nama Segmen Tangse dengan pola sesar menganan. Distribusi Gempa juga
menunjukkan adanya sub-segmen dengan dengan pola sesar normal di bagian utara Segmen
Tangse. Distribusi gempa di sepanjang Patahan Pidie Jaya timur laut -barat daya memiliki pola
sesar mengiri (sinistral strike slip).
Kata Kunci: gempa bumi, Patahan Sumatra, dense seismic network, relokasi, double
difference, mekanisme fokal

The Sumatran Fault is a dextral strike slip fault system that can be divided into several segments. The historical of earthquakes in northern Sumatra indicates the presence of secondary faults and segmentation in the north and south of the Sumatran fault. This study aims to delineate the Sumatran fault and segmentation based on high accuracy local earthquakes and focal mechanisms. A total 147 dense seismic network were installed in northern Sumatra, registering 3693 local earthquakes between December 2019 – June 2020 which were determined using HYPO71 based on recorded P and S waves. Initial earthquake relocation (VELEST) was applied to improve data quality, 2463 earthquakes were selected with azimuthal GAP≤190o and RMS < 0.5 s. Earthquake locations were improved by using a Double-Difference Method to get a detailed fault lineation. Detail interpretation of fault lineation and orientation were combined with focal mechanism by first polarity method and digital elevation model. The distribution of the earthquakes shows that the Seulimeum Fault lineation is segmented in the north, named Seulimeum-West and Seulimeum-North were identified as dextral strike-slip on both sides of the basin and a normal fault on the Pulau Weh. The Central Segment of The Seulimeum fault is lined along the southern of Seulawah volcano were identified as a dextral strike-slip fault and The Seulimeum Fault is segmented in the south by Seulimeum-South thrust fault and dextral strike-slip. The cluster in the southern Aceh segment were identified as the Jantho Fault with a normal fault. The Tangse segment were identified as a dextral strike-slip fault and the parallel and perpendicular sub-segments indicate the creeping zone is complicated where this area requires more detailed study. The distribution of the earthquake along the northeast-southwest Pidie Jaya fault were identified as a left fault (sinistral strike slip). Keywords: earthquakes, Sumatran Fault, dense seismic network, relocation, double difference, focal mechanism