Ground Motions, Site Amplification and Building Damage at Near Source of the 2006 Yogyakarta, Indonesia Earthquake

The objective of this study is to ascertain the causes of damage to buildings that occurred due to an earthquake near its source, particularly in the Pleret sub-district in Yogyakarta Special Province Indonesia. This study was conducted because a large percentage of human fatalities and structural collapse occurred during the Yogyakarta earthquake of May 27, 2006. Since the earthquake records on the site are not available, another way to obtain synthetic ground motions can be done in ways suggested by Bulajic and Manic (Motion records as a seismological input for seismic safety evaluation engineering structures, 2005), Rezaeian and Kiureghian (Earthq Eng Struct Dyn 39:1155–1180, 2010). Towards these ends, this research applied the Total Probability Theorem in the Seismic Hazard Probability Analysis (PSHA) with 3-D seismic sources. In this case, the PSHA analysis was carried out based on a 10% probability exceeded for 50 years building life time. The obtained uniform hazard spectrum (UHS) was then transferred to the risk targeted Maximum Credible Earthquake MCEr through the directivity factor D_f and risk targeted factor R_f with an average increase of 8.13% to UHS. Three earthquake records were selected, and after spectral matching, the high ranging bedrock accelerations were obtained from 0.254 to 0.289 g. After conducting site response analysis, peak ground accelerations on the ground surface varied from 0.398 to 0.412 g. Furthermore, acceleration site amplifications between 1.401 and 1.426 were obtained, which are higher than the spectral site amplification between 1.215 and 1.385. Since the site amplification is still in the normal category, building damage is mostly caused by relatively high levels of ground acceleration and shaking to relatively old buildings with low material and construction quality. Although the study is still in its early stages, there are indications of fling effects on the site even though the intensity is relatively small.