Analisis Travel Time Delay Untuk Kasus Tsunami Lintas Samudra

Abstract

Abstrak

Waktu kedatangan gelombang tsunami dan time delay di lokasi tertentu merupakan isu penting terkait dengan studi mitigasi bencana. Time delay dihitung dari perbedaan waktu antara observed travel time dan estimated travel time. Observed travel time diperoleh dari instrumen DART buoys dan tide gauges sedangkan estimasi waktu tempuh perambatan gelombang tsunami diperoleh dari solusi asumsi kecepatan gelombang panjang. Dalam penelitian ini, time delay dihitung untuk 3 kasus tsunami lintas samudra, yaitu Tohoku 2011, Sumatra 2012, dan Iquique-Chili 2014. Untuk semua kasus yang dipelajari, temuan penting adalah time delay meningkat secara linier dengan pertambahan jarak episentral. Hal itu menunjukkan bahwa kecepatan tsunami berkurang selama propagasi setidaknya karena dua faktor, yaitu variasi topografi dan batimetri dasar laut dan serta stratifikasi laut. Reduksi kecepatan tsunami untuk 2 kasus tsunami di Samudra Pasifik berada pada kisaran 1,3-1,4% sedangkan kasus tsunami di Samudra Hindia reduksi kecepatan ditemukan sebesar 4% karena kompleksitas batimetri dan topografi.

Kata Kunci: time delay, estimasi waktu tempuh, reduksi kecepatan tsunami

Abstract

Tsunami arrival time and its corresponding time delay at a particular location or station has been an important issue in recent years. The delay in time is calculated from a difference in arrival times between observed and estimated travel times. While the observed travel times were obtained from records of DART buoys and gauge stations, the predicted travel times were derived from the basic solution for a long wave speed of propagating tsunami. In this study, we estimated time delay for trans-oceanic tsunamis, that is, 2011 Tohoku, 2012 Sumatra, and 2014 Iquique-Chili occurrences. We found for all cases that the delay increases linearly with increasing epicentral distance. It follows that tsunami speed is reduced during propagation due to at least two possible factors. These factors include varying ocean floor topography and ocean stratification. Speed reduction for 2 cases in the Pacific Ocean is lying in the range 1,3-1,4% whereas the case in the Indian Ocean takes a bit larger for the reduction in speed by 4%, owing to complex bathymetry and topography.

Keywords: time delay, observed travel time, estimated travel time, reduced speed