Analisis Zona Rentan Rekahan Permukaan dan Kajian Rencana Tata Ruang Wilayah (RTRW) Gresik, Jawa Timur Berdasarkan Data Mikrotremor

Sulandari, Prof. Dr. Sismanto, M.Si

2025 | Tesis | S2 Ilmu Fisika

Penelitian ini menganalisis kerentanan seismik dan potensi zona rekahan tanah di wilayah pesisir timur Kabupaten Gresik, Jawa Timur, menggunakan data mikrotremor. Fokus kajian meliputi parameter amplifikasi gelombang, indeks kerentanan seismik, percepatan gerakan tanah (PGA), ground shear strain (GSS), kecepatan gelombang geser, dan ketebalan sedimen.

Wilayah Gresik memiliki risiko gempa tinggi akibat aktivitas seismik aktif, dengan nilai a-value 5,57 dan b-value 0,8–0,9 yang mengindikasikan potensi gempa besar. Ancaman ini diperparah oleh dominasi kawasan industri dan permukiman padat di pesisir, sehingga analisis risiko seismik menjadi krusial untuk mitigasi bencana dan perencanaan tata ruang adaptif. Metode mikrotremor (HVSR dan array) diterapkan untuk mengkarakterisasi dinamika tanah, sedangkan penilaian risiko seismik menggunakan pembobotan Simple Additive Weight (SAW). Data yang diperoleh diklasifikasikan berdasarkan SNI 1726:2019 untuk memetakan tingkat kerentanan.

Hasil penelitian menunjukkan variasi parameter kerentanan: amplifikasi (1,5–10,2), indeks kerentanan seismik (3,8–144,5), PGA (38–68 gal), GSS (0,1×10?³–8,1×10?³), dan ketebalan sedimen (24–109 meter). Zona risiko tertinggi (Kategori I) teridentifikasi di sekitar antiklin Sekarkurung, meliputi Kec. Gresik, timur Kebomas, tenggara Manyar, timur Cerme, dan sebagian utara Surabaya. Sementara wilayah barat daya Manyar hingga barat Cerme termasuk kategori risiko rendah-sedang (Kategori I–IV). Temuan ini menjadi dasar rekomendasi mitigasi dan perencanaan tata ruang berbasis risiko.

 

This study analyzes seismic vulnerability and potential soil fracture zones in the eastern coastal region of Gresik Regency, East Java, using microtremor data. The research focuses on parameters such as wave amplification, seismic vulnerability index, peak ground acceleration (PGA), ground shear strain (GSS), shear wave velocity, and sediment thickness.

Gresik is a high-risk earthquake zone due to active seismic activity, with an a-value of 5.57 and b-value of 0.8–0.9, indicating the potential for major earthquakes. This threat is exacerbated by the dominance of industrial areas and dense residential zones along the coast, making seismic risk analysis crucial for disaster mitigation and adaptive spatial planning. The microtremor method (HVSR and array) was applied to characterize soil dynamics, while seismic risk assessment was conducted using the Simple Additive Weighting (SAW) method. The obtained data were classified according to SNI 1726:2019 to map vulnerability levels.

The results reveal variations in vulnerability parameters: amplification (1.5–10.2), seismic vulnerability index (3.8–144.5), PGA (38–68 gal), GSS (0.1×10?³–8.1×10?³), and sediment thickness (24–109 meters). The highest-risk zone (Category I) was identified around the Sekarkurung anticline, encompassing Gresik District, eastern Kebomas, southeastern Manyar, eastern Cerme, and parts of northern Surabaya. Meanwhile, the southwestern Manyar to western Cerme areas were classified as low-to-medium risk (Categories I–IV). These findings serve as a basis for risk-based mitigation recommendations and spatial planning.

 

Kata Kunci : Mikrotremor, Rekahan, Kerawanan Seismik, Simple Additive Weight