Harsuko, M.R.C., Zulfakriza, Z., Nugraha, A. D., Muzli, M., Sahara, D.P.Puspito, N.T. , Husni, Y.M. , Prabowo B.S. , Sarjan, A.F.N.
Jurnal Geofisika
(2020) Vol.18, No.01 pp. 01-06
In 2018, Lombok Island was hit by a series ofdestructive earthquakes. According to Indonesian Meteo-rological, Climatological, and Geophysical Agency data,about 1,973 felt earthquakes (M>3) which shaken Lombokwere recorded during August 2018 with three earthquakeswith the largest magnitude of 6.9 Mw, 6.8 Mw, and 6.2Mw. National Board for Disaster Management reportedabout 555 deaths, 1,833 people injured, and 186,010houses damaged as a result of Lombok earthquake onAugust 5th, 2018. A number of seismometers were placedon Lombok Island from August 3rd, 2018 to October19th, 2018 to monitor the aftershock events. There are17 stations that record seismicity in Lombok consistingof 10 broadband sensors and 7 short period sensors. Inthis study, we used the Horizontal-to-Vertical SpectralRatio (HVSR) method to analyze the risk of earthquakein the Lombok region. The basic concept of this methodis to do a comparison between the horizontal componentspectrum and the vertical component spectrum of a wave,where theoretically the particle movement of the horizontalcomponent is greater than the particle movement of thevertical component on soft ground, whereas on the hardground both components (horizontal and vertical) willbe similar. H/V curve obtained from earthquake record-ings (Earthquake Horizontal-to-Vertical Ratio/EHVR)and H/V curve obtained from microtremor recordings(Microtremor Horizontal-to-Vertical Ratio/MHVR) showsgood agreement and high correlation. Empirical correctionof EMR (Earthquake-to-Microtremor Ratio) managedto decrease the difference of estimation of predominantfrequency and amplification factor between EHVR andMHVR. Predominant frequency, amplification, and seismicvulnerability map agree with the geological condition of Lombok Island, where high value of amplification andseismic vulnerability was found on soft and thick ground.This study conclude that the maximum ground accelerationand the construction of the building should also consideredwhen one wants to investigate the effect of an earthquake tothe damage occurred, beside the site effects.
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