STUDI KARAKTERISTIK GEMPABUMI SIGNIFIKAN MW > 6.0 AKIBAT AKTIVITAS SISTEM BUSUR BELAKANG SEGMEN BALI LOMBOK MENGGUNAKAN ANALISIS ENERGI KUMULATIF DAN PERIODE ULANG

Abstract

Analisis energi dan periode ulang gempabumi akibat aktivitas sistem busur belakang Flores dilakukan untuk mengetahui besarnya energi yang telah dilepaskan serta menghitung periode ulang gempabumi yang akan terjadi disertai kemungkinan energi yang akan dilepaskan oleh gempabumi di masa yang akan datang. Data yang digunakan adalah katalog gempabumi International Seismological Centre (ISC), Engdahl-van der Hilst-Buland (EHB) dan Badan Meteorologi Klimatologi dan Geofisika (BMKG) tahun 1963-2018. Daerah penelitian dibatasi pada daerah dengan rentang 7,5 LS – 8,5 LS dan 115 BT – 117 BT. Perhitungan energi gempabumi didapatkan dengan mengkonversikan nilai momen seismik kedalam energi fisis gempabumi. Sedangkan nilai momen seismik didapatkan dari konversi magnitudo gempabumi. Nilai periode ulang didapatkan dengan membagi nilai slip rata-rata terhadap sliprate. Dengan asumsi bahwa energi seismik potensial yang tersimpan pada sistem busur belakang Flores segmen Bali-Lombok setara dengan gempabumi Mw 7,4 dan energi seismik yang telah terlepas selama periode 1963-2018 setara dengan gempabumi Mw 7,3, maka selisih atau sisa energi seismik yang masih tersimpan setara dengan Mw 7,0. Sedangkan hasil perhitungan periode ulang gempabumi signifikan Mw 6,7 – Mw7,1 berkisar antara 117 tahun hingga 201 tahun.

The analysis of seismic energy and return period of the earthquakes due to the Flores back arc thrust fault system were conducted to determine the amount of the seismic energy that has been released and to estimate the return period and potential energy of the significant earthquakes which may occur in the future. The data used in this study were retrieved from the earthquake catalogs of the International Seismological Centre (ISC), Engdahl-van der Hilst-Buland (EHB) dan The Agency for Meteorology, Climatology, and Geophysics of the Republic of Indonesia (BMKG) between 1963 to 2018. The research area is restricted to the range of 7.5 LS - 8.5 LS and 115 BT - 117 BT. The earthquake energy was obtained by converting the values of a seismic moment into the physical energy of the earthquake. Whereas, the seismic moment value was obtained using the empirical formulas which show the relation between seismic moment and magnitude of the earthquake. The return period of the earthquakes has been done by dividing the average slip of the specific earthquake against the slip rate of the fault system. By making the assumption that the potential seismic energy which stored in the Flores back arc thrust fault system, segment Bali-Lombok, is equal to the earthquake Mw 7.4, while the seismic energy which has been released is equal to the earthquake Mw 7.3. We estimate the remaining seismic potential energy is equal to the earthquake Mw 7.0. Whereas the return period of the significant earthquakes Mw 6.7 – Mw 7.1 is about 117 to 201 years.