Seismisitas Pulau Sumatera dan Wilayah Sekitarnya Akibat Aktivitas Seismo-Tektonik Zona Subduksi dan Patahan
Seismicity of Sumatra Island and Its Surrounding Areas Due to Seismo-Tectonic Activity of the Subduction Zone and Faults
Penelitian ini bertujuan untuk menganalisis seismisitas di Pulau Sumatera dan wilayah sekitarnya, mengingat wilayah ini merupakan salah satu kawasan dengan aktivitas gempa yang tinggi akibat kondisi geologi dan tektonik yang kompleks. Seismisitas wilayah dapat dipelajari melalui distribusi frekuensi-magnitudo (FMD) untuk estimasi tiga parameter seismik, yaitu Mc, b-value, dan a-value. Data gempa diperoleh dari katalog ISC–GEM (1924–2024) dengan magnitudo 4,0 ≤ Mw ≤ 9,5. Estimasi ketiga parameter dilakukan dengan bantuan ZMAP7.0 dan Matlab2018a berdasarkan enam zonasi seismik: Zona 1 dan Zona 2 (wilayah utara Sumatera), Zona 3 dan Zona 4 (wilayah tengah Sumatera) serta Zona 5 dan Zona 6 (wilayah selatan Sumatera). Kedalaman sumber gempa diklasifikasikan: shallow sources dan intermediate sources. Data statistik gempa kemudian diolah menjadi raw data, converted data dan filtered data. Hasil analisis menunjukkan bahwa aktivitas seismik di Pulau Sumatera dan wilayah sekitarnya didominasi oleh gempa dangkal, dengan nilai a-value lebih tinggi di zona barat Sumatera, terutama di Zona 3 (6,02), mengindikasikan tingkat seismisitas lebih intens. Sebaliknya, zona timur Sumatera memiliki nilai a lebih rendah, mencerminkan aktivitas seismik yang lebih stabil. Nilai b di keenam zona seismik berada dalam rentang ≈ 0,4–0,9 mengindikasikan struktur batuan bawah permukaan wilayah studi mengalami stres tektonik tinggi. Nilai b yang rendah di zona barat, menandakan potensi akumulasi energi seismik yang signifikan dan risiko gempa besar di masa depan. Hubungan antara Mc, b, dan a memberikan gambaran karakteristik sumber gempa, serta mendukung pemodelan probabilistik dan penentuan prioritas mikrozonasi di wilayah rawan.
This study aims to analyze seismicity in Sumatra Island and its surrounding regions, considering that this area experiences high earthquake activity due to its complex geological and tectonic conditions. The seismicity is examined through the frequency-magnitude distribution (FMD) to estimate three seismic parameters: Mc, b-value, and a-value. Earthquake data were obtained from the ISC–GEM catalog (1924–2024) with magnitudes ranging from 4,0 ≤ Mw ≤ 9,5. Parameter estimation was performed using ZMAP7.0 and MATLAB 2018a based on six seismic zones: Zone 1 and Zone 2 (northern Sumatra), Zone 3 and Zone 4 (central Sumatra), and Zone 5 and Zone 6 (southern Sumatra). The earthquake source depths were classified into shallow and intermediate sources. The seismic data were processed into raw, converted, and filtered datasets. The analysis results indicate that seismic activity in Sumatra and its surroundings is dominated by shallow earthquakes, with higher a-values observed in the western zones, particularly Zone 3 (6.02), indicating more intense seismicity. Conversely, the eastern zones exhibit lower a-values, reflecting more stable seismic activity. The b-values across all six zones range from approximately ≈ 0.4 to 0.9, suggesting that the subsurface rock structures in the study area experience high tectonic stress. Lower b-values in the western zones imply significant accumulation of seismic energy and the potential risk of large earthquakes in the future. The relationship between Mc, b, and a provides insights into the characteristics of earthquake sources and supports probabilistic earthquake modeling and the prioritization of microzonation efforts in hazard-prone areas.