Karakteristik Faktor Penguatan Gelombang Gempabumi oleh Lapisan Lunak Permukaan, Studi Kasus di Wilayah Perkotaan Cianjur dan Sekitarnya

Marjiyono, Marjiyono
Hidayat, Hidayat
Hamidah, Nimas Nurul
Hawan, Shofi Iqtina
Setiawan, Johannes Bosco Januar Herry
Andriani, Shofi

Jurnal Geologi dan Sumberdaya Mineral (Journal of Geology and Mineral Resources)
Vol. 26 No. 4 (2025)

Disamping dekat dengan sumber gempabumi, wilayah perkotaan Cianjur juga beresiko terhadap penguatan gelombang gempabumi oleh lapisan lunak litologi permukaan. Endapan soil yang cukup tebal di kawasan ini berpotensi menguatkan gelombang ketika terjadi gempabumi. Hasil pemodelan data mikrotremor array di 18 titik ukur diperoleh kecepatan gelombang geser soil berkisar antara 50 m/det. - 308 m/det. Endapan soil ini menumpang di atas batuan vulkanik yang memiliki kecepatan gelombang geser antara 246 m/det – 1415 m/det. Adapun ketebalan soil berdasarkan pemodelan data mikrotremor single station di 189 titik ukur berkisar antara 2 m – 62 m. Nilai faktor penguatan gelombang oleh lapisan soil ini berkisar antara 1 - 2,4 kali dengan zona penguatan tinggi berada di daerah Cugenang, Warungkondang dan Cilaku. Berdasarkan catatan, ketiga wilayah tersebut mengalami intensitas goncangan maksimum sebesar VIIVIII skala MMI. Kata kunci: penguatan gelombang, lapisan lunak permukaan, mikrotremor array, mikrotremor single station. Abstract The Cianjur urban area is exposed to a substantial risk, particularly near the seismic source and due to site amplification, resulting from a soft surface layer. The fairly thick soil deposits potentially amplify seismic waves when an earthquake occurs. According to the microtremor array that was deployed on 18 locations, soil shear wave velocity ranges from 50 m/sec to 308 m/sec. This soil deposit lies above volcanic rock that has shear wave velocities ranging from 246 m/s to 1415 m/s. Single-station microtremor data modelling on 189 sites revealed that the soil thickness varies between 2 m and 62 m. The calculated site amplification of the research area ranges from 1 to 2.4 times, indicating that the Cugenang, Warungkondang, and Cilaku regions have significant amplification zones. Historical records showed that the highest shaking intensity in the three regions ranged from VII to VIII of the MMI scale. Keywords: site amplification, soft surface layer, array microtremor, single station microtremor