MIKROZONASI SEISMIK DI WILAYAH ANCAMAN SESAR LEMBANG ANTARA SEKSI CIHIDEUNG DAN GUNUNG BATU BERDASARKAN PENGUKURAN MIKROTREMOR

Reza Fahrurijal, Adrin Tohari, Imamal Muttaqien

Abstract


Sesar Lembang merupakan salah satu sesar aktif yang mengancam wilayah Jawa Barat. Upaya pengurangan risiko dari ancaman sesar ini memerlukan pengetahuan mengenai tingkat kerentanan seismik di wilayah yang berada di zona sesar. Makalah ini menyajikan hasil analisis rasio spektral H/V dari data pengukuran mikrotremor di sepanjang zona Sesar Lembang, antara Seksi Cihideung dan Gunung Batu, untuk menghasilkan mikrozonasi kerentanan seismik di wilayah Kecamatan Lembang dan Parongpong. Hasil analisis menunjukkan bahwa wilayah Kecamatan Lembang dan Parongpong yang tersusun oleh lapisan endapan danau dan pasir tufan, umumnya dicirikan oleh nilai frekuensi dominan yang rendah dan faktor amplifikasi sedang hingga tinggi. Berdasarkan indeks kerentanan seismik, kedua kecamatan ini secara umum dapat diklasifikasikan sebagai daerah dengan kerentanan seismik yang tinggi. Akan tetapi, daerah yang terbentuk dari lapisan breksi tua di Kecamatan Lembang memiliki kerentanan seismik yang rendah, sedangkan daerah-daerah di wilayah Kecamatan Parongpong di sepanjang Seksi Cihideung yang tersusun oleh lapisan pasir tufan merupakan daerah dengan kerentanan seismik sedang. Dengan demikian, kerentanan seismik wilayah ancaman Sesar Lembang sangat spesifik di setiap daerah dan dipengaruhi oleh jenis satuan litologi.

ABSTRACT - Seismic microzonation of Lembang Fault hazard area along Cihideung and Gunung Batu sections using microtremor measurements

Lembang Fault is amongst the active faults that pose a significant threat to the West Java region. Mitigation efforts in reducing seismic risks associated with this fault require knowledge of seismic vulnerability in the area along the fault zone. This paper presents the results of horizontal to vertical (H/V) spectral ratio analysis of microtremor data across the Lembang Fault zone, measured along the Cihideung and Gunung Batu Sections, to establish a seismic vulnerability microzonation of Lembang and Parongpong Subdistricts. The study shows that the Lembang and Parongpong Sub-district areas composed of lake sediments and tuffaceous sand units are generally characterized by low dominant frequencies and medium to high amplification factors. According to their seismic vulnerability indices, in general, these two subdistricts can be classified as areas with high seismic vulnerability. However, the areas covered by the old breccia unit in the Lembang Sub-district have low seismic susceptibility, while the areas covered by the tuffaceous sand unit along the Cihideung Section in Parongpong Subdistrict have the medium seismic vulnerability. Thus, this study indicates that the seismic vulnerabilities of Lembang Fault hazard area are considerably site-specific and influenced by the lithology.


Keywords


Amplification factor, dominant frequency, horizontal to vertical spectral ratio, Lembang Fault, microtremor, seismic vulnerability index

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DOI: http://dx.doi.org/10.14203/risetgeotam2020.v30.1092

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