Microzonation Analysis Using the Microsroseismic MethodBased on Soil Vulnerability Index and Ground Profiles Valueof Wave Speed in Piyungan District, Bantul Regency, SpecialRegion of Yogyakarta
Indriati Retno Palupi, Ditto Octa Saputra, Ajimas Pascaning S, Dian Susri Nurhaci

1Departement of Geophysical Engineering, Universitas Pembangunan Nasional Veteran Yogyakarta, Indonesia
Jl. SWK No. 104, Ngropoh, Condongcatur, Depok Subdistrict, Sleman Regency, Special Region of Yogyakarta 55283
2Meteorology Climatology and Geophysics Agency Yogyakarta, Indonesia
Jl. Wates KM 8 Jitengan Balecatur, Gamping Subdistrict,, Sleman Regency, Special Region of Yogyakarta 55295

Abstract

Yogyakarta is one of the earthquake-prone areas because it lies near subduction area, the last recorded occurrence of large intensity earthquake activity on 2006, May 27th had a magnitude of 5.9 SR (Richter Scale) and suffered considerable damage. The Department of Social Affairs said that 6,234 people died, 36,299 people were injured and about 1.5 million people were displaced by the earthquake. The earthquake also caused damage to 616,458 residential building units in Yogyakarta and Central Java. Under the USGS, the epicenter of the earthquake is about 25 km southeast of Yogyakarta with a depth of 17.1 km below sea level. Microtremor data with HVSR (Horizontal to Vertical Spectral Ratio) method can be used to determine the value of the predominant frequency spectrum (fo) and amplification factor (A) which describes the dynamic characteristics of the soil. The HVSR analysis method was developed to calculate the ratio of the Fourier spectrum of the microtremor signal to the horizontal component against its vertical component. Calculations regarding the value of soil vulnerability and analysis of subsurface structures are intended to determine the level of vulnerability of an area to earthquake hazards. In the Piyungan sub-district the thickness of the sediment layer (H) ranges from 5 meters to 75 meters below the surface. The northern part of Piyungan sub-district tends to have a thick layer of sediment which is quite thick reaching 45 meters to 75 meters. While the value of the soil vulnerability index in most of the northern part of the study area has a land vulnerability index value that tends to be greater than 40 x 10-6 s2/cm with a maximum value of 78.62 x 10-6 s2/cm. Most of the study areas have soft soil types (Vs < 175 m/s), medium soils (175 m/s < Vs ≤ 350 m/s) and very dense soils and soft rocks (350 m/s < Vs ≤ 750 m/s).

Keywords: Microsroseismic, Horizontal to Vertical Spectral Ratio,Ellipticity Curve, Sediment Layer Thickness.

Topic: Geophysics,Geomatics and Geochemistry

Link: https://ifory.id/abstract-plain/kD7raBteNHng

Web Format | Corresponding Author (Ajimas Pascaning Setiahadiwibowo)