ANALISIS DISTRIBUSI TEGANGAN NORMAL GEMPA BUMI DI WILAYAH SESAR SUMATRA MENGGUNAKAN METODE INVERSI TEGANGAN
ANALYSIS OF NORMAL STRESS DISTRIBUTION EARTHQUAKE IN THE SUMATRA FAULT ZONE USING STRESS INVERSION METHOD
Sumatra merupakan salah satu wilayah dengan aktivitas tektonik tertinggi di Indonesia. Sumatra dilalui oleh patahan aktif yang membentang sejauh 1900 km sepanjang Bukit Barisan sampai Aceh utara yang disebut sesar Sumatra. Aktivitas tektonik pada daerah rawan gempa dapat diketahui melalui kajian distribusi posisi dan arah tegangan normal gempa bumi bahkan adanya aktivitas tektonik susulan. Tegangan normal dapat memicu maupun menghambat suatu patahan. Untuk mengetahui distribusi posisi dan arah tegangan normal digunakan metode inversi tegangan di wilayah sesar Sumatra dengan memasukkan 54 data sekunder parameter bidang sesar (strike, dip, rake) yang diakses bebas melalui laman CMT IRIS database gempa bumi ke dalam software stressinverse. Hasil yang diperoleh berupa gambar yang menginterpretasikan posisi dan arah tegangan normal gempa bumi yang meliputi diagram lingkaran Mohr, persebaran sumbu P dan T, histogram rasio bentuk, dan arah tegangan utama. Gambar persebaran sumbu P dan T menunjukkan distribusi posisi tegangan normal maksimum (σ1), intermediate (σ2), dan minimum (σ3) pada wilayah sesar Sumatra, sedangkan gambar arah tegangan utama menunjukkan arah tegangan normal pada sesar Sumatra. Tegangan normal maksimum menandakan adanya aktivitas seismik tinggi yang mendominasi sesar Sumatra area utara. Tegangan intermediate mendominasi sekitar sesar Sumatra. Area timur sesar Sumatra didominasi oleh tegangan normal minimum. Nilai histogram rasio bentuk mendekati 0.8 menandakan kesesuaian data terhadap teori Vavrycuk dengan nilai rasio minimum 0.7 dan nilai rasio maksimum 1. Kualitas data parameter bidang sesar yang sesuai dengan karakteristik sesar wilayah penelitian sangat mempengarui diagram histogram rasio bentuk.
Sumatra is one of the regions with the highest tectonic activity in Indonesia. Sumatra has passed by an active fault that stretches for 1900 km along the Bukit Barisan to North Aceh is called the Sumatra fault zone. Tectonic activity in earthquake-prone areas can be identified through normal stress studies and even subsequent tectonic activity. Normal stresses can trigger or inhibit a fault. To determine the distribution of the normal stress position and direction, the stress inversion method is used in the Sumatra Fault area by entering 54 secondary data on the fault plane parameters (strike, dip, rake) which is freely accessed through the CMT IRIS earthquake database page into stressinverse software. The results obtained are images that interpret the position and direction of normal earthquake stresses which include Mohr pie chart, distribution of P and T axis, shape ratio histogram, and principal stress direction. Distribution of P and T axis image shows the distribution of the maximum (σ1), intermediate (σ2), and minimum (σ3) normal stress positions in the study area, while the main stress direction image shows the normal stress direction on the Sumatran fault. The maximum normal stress indicates the presence of high seismic activity that dominates the northern Sumatra fault. The intermediate stress dominates around the Sumatra fault. The eastern area of the Sumatra fault is dominated by the minimum normal stress. The shape ratio histogram value is close to 0.8 indicating the suitability of the data to Vavrycuk's theory with a minimum ratio value of 0.7 and a maximum ratio value of 1. The quality of the fault plane parameter data according to the fault characteristics of the study area greatly influences the shape ratio histogram diagram.