Determining Earthquake Susceptible Areas Southeast of Yogyakarta, Indonesia—Outcrop Analysis from Structure from Motion (SfM) and Geographic Information System (GIS)

Abstract

Located approximately a hundred kilometres north of Java Subduction Zone, Java Island has a complicated geology and geomorphology. The north zone is dominated by the folded area, the centre is dominated by the active volcanic arc and the south of Java including the study area (Southeast part of Yogyakarta City), is dominated by the uplifted southern mountain. In general, the study area is part of the Bantul's Graben. In the middle part of study area flows the Opak River, which is often associated with normal faults of Opak Fault. The Opak Fault is such a complex fault system which has a complex local fault which can cause worst local site effect when earthquakes occur. However, the geology map of Yogyakarta is the only data that gives the characteristics of Opak Fault roughly. Thus, the effort to identify unchartered fault system needs to be done. The aims of this study are to conduct the outcrop study, to identify the micro faults and to improve the understanding of faults system to support the earthquake hazard and risk assessment. The integrated method of remote sensing, structure from motion (SfM), geographic information system (GIS) and direct outcrop observation was conducted in the study area. Remote sensing was applied to recognize the outcrop location and to extract the nature lineament feature which can be used as fault indicator. The structure from motion was used to support characterising the outcrop in the field, to identify the fault evidence, and to measure the fault displacement on the outcrops. The direct outcrop observation is very useful to reveal the lithofacies characteristics and to reconstruct the lithostratigraphic correlation among the outcrops. Meanwhile, GIS was used to analyse all the data from remote sensing, SfM, and direct outcrop observation. The main findings of this study were as follows: the middle part of study area has the most complicated geologic structure. At least 56 faults evidence with the maximum displacement of 2.39 m was found on the study area. Administratively, the north part of Segoroyoso Village, the middle part of Wonolelo Village, and the middle part of Bawuran village are very unstable and vulnerable to the ground motion amplification due to their faults configuration. The further studies such as geo-electric survey, boreholes survey, and detail geological mapping still need to be conducted in the study area to get better understanding of Opak Fault. Additionally, the carbon testing of charcoal that found in the outcrop and identification of exact location of the ancient eruption source also need to be done.

Workflow: From photo-based 3-D reconstruction of remotely piloted aircraft images to a 3-D geological model

“…In geology, photo-based 3-D reconstruction of RPA data is mostly used for small (<2 km 2 ) areas, such as for monitoring coastal topographic changes (Mancini et al, 2013;Gonçalves and Henriques, 2015), studying landslides (Niethammer et al, 2012;Lucieer et al, 2014) and lava flows (Carr et al, 2019), and mapping geological outcrops and structures (Favalli et al, 2012;Bemis et al, 2014;Vasuki et al, 2014;Johnson et al, 2014;Bistacchi et al, 2015;Chesley et al, 2017;Piras et al, 2017;Saputra et al, 2017Saputra et al, , 2018Corradetti et al, 2018;Fleming and Pavlis, 2018;Madjid et al, 2018). This method has huge potential for efficient large-scale (>2 km 2 ) geological mapping, where there is substantial geologic exposure, when compared to ground-based techniques (Brush et al, 2018).…”

Site Coefficient of Short Fa and Long period Fv Maps Constructed from the Probabilistic Seismic Hazard Analysis in Yogyakarta Special Province

“…Another major earthquake that occurred in Yogyakarta was on 23 July 1943 with coordinates of the epicenter of 8.6S, 109.9E The earthquake had a magnitude of M7.1, with a depth of 60 km and the coordinates of the epicenter were 8.6S and 109.9E [5]. The earthquake had caused as many as 213 fatalities and more than 12,000 houses were damaged starting from Garut, south coast of Central Java, Yogyakarta, and Surakarta.…”

“…In YSP, the Opak faults were not well known before May 27th, 2006 Yogyakarta earthquake. According to [22] the 27th may 2006 Yogyakarta earthquake was caused by the activity of oblique Opak fault with strike-slip of 0.8m, dip-slip of -0.26m and strike N 48o to E. The slip-rate of Opak fault is about 2.4 mm/year with the maximum historical earthquake magnitude of Mw6.8 [4,5], According to [23] the Opak fault has a dip angle of 87 o ; rake angle of 177 o (right lateral strike-slip) and the upper edge of the fault (ZTOR) at 6 km. The Opak, Lasem, Pati, and Bumiayu faults are the active faults that are taken into account in this analysis.…”

Earthquake Triggered Multi-Hazard and Risk Study Based on Remote Sensing and Geographic Information System

“…2). [8] stated that Pleret Sub-District is located in the eastern Horts of Bantul Graben which was experienced by step faults due to the complexity of specific geological structure.…”

“…Both of these formations were generated from the eruption of surrounding ancient volcano [9][10][11]. Furthermore, [8] found that both Tmse and Tmn can be classified as pyroclastic density flow from the ancient volcano that might be located in the east part of the study area.…”