THE CHANGE OF ROCK CONDITION OBSERVED BY H/V SPECTRAL AND ELLIPTICITY CURVE INVERSION ANALYSIS (CASE STUDY: PALU EARTHQUAKE SEPTEMBER 28, 2018)

  • Sandy Tri Gustono Geophysics Department, College of Meteorology Climatology and Geophysics Perhubungan 1 Street, Number 5, Pondok Betung, Pondok Aren, Tangerang Selatan City, Banten, 15221, Indonesia
  • Muhammad Akhadi
  • Kekey Salsabil Azzahra Geophysics Department, College of Meteorology Climatology and Geophysics Perhubungan 1 Street, Number 5, Pondok Betung, Pondok Aren, Tangerang Selatan City, Banten, 15221, Indonesia
  • Rika Adelina Ginting Geophysics Department, College of Meteorology Climatology and Geophysics Perhubungan 1 Street, Number 5, Pondok Betung, Pondok Aren, Tangerang Selatan City, Banten, 15221, Indonesia
Keywords: palu earthquake, microtremor, HVSR method, seismic vulnerability, Vs30

Abstract

Palu City is composed of sedimentary rocks so that it has a high level of vulnerability when an earthquake occurs. The earthquake that occurred on September 28, 2018, 25 km north of Donggala with a magnitude of 7.4 Mw, had caused a tsunami that struck Palu City, Sigi Regency, Donggala Regency, and Parigi Mouthong Regency, Central Sulawesi Province. This earthquake also caused liquefactions in the Petobo and Balaroa areas, Palu City, and Jono Oge in Sigi Regency. In this study, the authors used microtremor data at 8 points measured before and after the earthquake. Processing using the Horizontal to Vertical Spectra Ratio method shows that the predominant frequency and amplification factor changes due to changes in local rock conditions. The analysis also shows the value of soil vulnerability index (Kg) mostly increased after the earthquake. Besides, the elliptic curve inversion method shows that before the earthquake event, the value of the S wave velocity (Vs30) in layer one was between 157.1-211.4 m/sec with a layer thickness between 65.3-90.6 meters, while after the earthquake, the velocity becomes 156-214.6 m/sec with a layer thickness ranging between 66-99.2 meters. This indicates that the area consists of soft and medium soils, which subsequently increased sediment thickness in most areas after the earthquake.

References

N. R. Hanifa and Supartoyo, “Tektonik Sulawesi,” in Kajian Gempa Palu Provinsi Sulawesi Tengah 28 September 2018 (M7,4), Tim Pusat Studi Gempa Nasional, Ed. Bandung, Indonesia: Pusat Penelitian dan Pengembangan Perumahan dan Permukiman, Badan Penelitian dan Pengembangan, Kementerian Pekerjaan Umum dan Perumahan Rakyat, pp. 9-15, 2018.

A. Soehaimi et al., “Peta Zonasi Kerentanan Bencana Gempabumi Daerah Palu dan Sekitarnya,” Bandung, Indonesia: Pusat Penelitian dan Pengembangan, Badan Geologi, 2000.

I. Meilano et al., “Tektonik Geodesi Indonesia,” in Peta Sumber dan Bahaya Gempa Indonesia Tahun 2017, Tim Pusat Studi Gempa Nasional, Ed. Bandung, Indonesia: Pusat Penelitian dan Pengembangan Perumahan dan Permukiman, Badan Penelitian dan Pengembangan, Kementerian Pekerjaan Umum dan Perumahan Rakyat, pp. 119-191, 2017.

W. F. Marcuson, “Definition of Terms Related to Liquefaction,” in Journal of The Geotechnical Engineering Division, vol. 104, no. 9, pp. 1197-1200, 1978.

W. Hermawan et al., “Sebaran Kerusakan Geologi Permukaan,” in Di Balik Pesona Palu, Bencana Melanda, Geologi Menata, A. W. Kusumah M. et al., Ed. Bandung, Indonesia: Badan Geologi, Kementerian Energi dan Sumber Daya Mineral, pp. 101-111, 2018.

J. Almendros et al., “Microtremor Analyses at Teide Volcano (Canary Island, Spain): Assessment of Natural Frequencies of Vibration Using Time-dependent Horizontal-to-vertical Spectral Ratios,” in Pure and Applied Geophysics, vol. 161, pp. 1579-1596, 2004.

Badan Informasi Geospasial. (2018). Pusat Pengelolaan dan Penyebarluasan Informasi Geospasial Badan Informasi Geospasial (BIG). Peta Terdampak Gempabumi dan Tsunami [Online]. Available: https://tanahair.indonesia.go.id/portal-web/bencana/metadata_sulteng.html

Y. Nakamura, “A Method for Dynamic Characteristics Estimation of Subsurface using Microtremor on the Ground Surface,” in Quarterly Report of RTRI, Vol. 30, no. 1, pp. 25-33, 1989.

C. Acerra, H. B. Havenith, and S. Zacharopoulos, “Guidelines for the Implementation of the H/V Spectral Ratio Technique on Ambient Vibration: Measurement, Processing and Interpretation,” SESAME European research project, European Commission-Research General Directorate, 2004.

N. Haerudin et al., “Earthquake Disaster Mitigation Mapping by Modeling of Land Layer and Site Effect Zone in The Kota Baru of South Lampung,” in Jurnal Pendidikan Al Biruni, Vol. 1, no. 8, 2019.

Y. Nakamura et al., “Local Site Effect of Kobe Based On Microtremor Measurement,” in Proceedings of the Sixth International Conference on Seismic Zonation (6 ISCZ) EERI, California, 2000.

H. C. Huang and Y. S. Tseng, “Characteristics of soil liquefaction using H/V of microtremors in Yuan-Lin Area, Taiwan,” in TAO, Vol. 13, no. 3, pp. 325-338, 2002.

A. Omang et al., “Menghitung Guncangan Gempabumi” in Di Balik Pesona Palu, Bencana Melanda, Geologi Menata, A. W. Kusumah M. et al, Ed. Bandung, Indonesia: Badan Geologi, Kementerian Energi dan Sumber Daya Mineral, pp 57-70, 2018.

A. Cipta and A. Solikhin, “Pendugaan Kecepatan Gelombang Permukaan (VS30) di Pulau Sulawesi Berdasarkan Klasifikasi Geomorfologi dan Aplikasinya,” in Jurnal Gunung api dan Mitigasi Bencana Geologi, vol. 3, no. 2, 2011.

Published
2020-12-31
How to Cite
Gustono, S. T., Akhadi, M., Azzahra, K. S., & Ginting, R. A. (2020). THE CHANGE OF ROCK CONDITION OBSERVED BY H/V SPECTRAL AND ELLIPTICITY CURVE INVERSION ANALYSIS (CASE STUDY: PALU EARTHQUAKE SEPTEMBER 28, 2018). Spektra: Jurnal Fisika Dan Aplikasinya, 5(3), 201 - 212. https://doi.org/10.21009/SPEKTRA.053.04