EGU General Assembly 2019 07th-12th April 2019 Vienna, Austria Sara Pena-Castellnou1*, Gayatri Indah Marliyani2, Klaus Reicherter1 Preliminary Tectonic Geomorphology of the Opak Fault System, Java (Indonesia) (1) Neotectonics and Natural Hazards, RWTH Aachen University, Aachen, Germany (2) Geological Engineering Department, Universitas Gadjah Mada, Yogyakarta, Indonesia Introduction Methods Results Channel Steepness Knickpoints Identification of active tectonic geomorphological We have calculated two morphometric indices: normalized 420000 430000 440000 450000 460000 435000 450000 435000 450000 features represents a challenge in slowly broad channel steepness index (Ksn) and spatial distribution of knickpoints, to integrate them with the geomorphology and Geological Units deforming areas that have tropical climates like Quaternary geology of the study area in order to map the Opak fault !( !( !( Java. Faults may be buried by thick sediments or Merapi deposits !( !( !( !( !(!( !( !( system. Our input data is the 8 m resolution DEMNAS digital Quaternary !( !( !( !( !( soils, land relief is low, and their geomorphic !( !( !( !( !( !( !( !( !( !( !( !( elevation model (http://tides.big.go.id/DEMNAS/). The !( !( Miocene !( !( expression such as fault scarps are eroded !( !( !( !( !( !( 9140000 9140000 !(!( (! !( !( !( !( !( !( !( Fm. Kepek !( !(!( !( !( !( analysis is perfomed using LSDTopoTools software (Mudd et !( !( !( !( quickly constraining it undetectable until the next !(!( !( !( !( !( !( !( Fm. Wonosari !( !( !(!( al., 2018) which is able to extract knickpoints from river !( !( 9135000 !( 9135000 earthquake (e.g. Marliyani et al., 2016). 9135000 9135000 !( !( !( Fm. Oyo !( !( !( !( !( !( !(!( profiles (Figure 4). !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( Fm. Sambipitu !(!( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !(!(!( !( This work focuses on the Opak Fault system, !( !( !( !( !( !( !( !( !( !( !( !( Fm. Nglanggran !( !( !( !( !(!( !( !( !( !( !( !( !( !( !( !( !( !(!( !( !( !( !( !( !( !( !( !( !( !( !( located in the central-southern part of Java, (A) !( !( !( !( !( !( Oligocene !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !(!(!( !( !( Indonesia (Figure 1) and thought to be the Fm. Semilir !( !(!(!( !( !( !( !(!(!( !( !( Digital !(!( !( !( !( !( !( !( !( !( 9130000 9130000 !( source of the devastating 2006 M 6.3 Yogyakarta Eocene !( !( !( !( !( !( !( !( !( !(!( Elevation Model !( !( !( !( !( !( Fm. Kebobutak !( !( !( !( !( !( !( !( !( !( earthquake. Here, we present a !( !(!(!( Mesozoic !( !(!( !( !( !( !( !( !( tectono-geomorphological analysis based on !( !( !(!(!(!( !( !( Basement !( !( !( !(!( !( !( !( !( !( !( !( !( !( !(!( !( morphometric indices of channel steepness !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( index and knickpoint identification in order to LSDTopoTools !( !( !( !( !( !( !( Legend !( !(!( !( map the Opak fault system as well as identifying 9120000 !( !( !( Knicpoints by inferred cause 9120000 1) Channel extraction (area threshold method) 9120000 9120000 !( !( !( !( !(!( !( other existing faults in the vicinity that may have !( !( !( !( River terrace !( !( 2) Select best-fit concavity index (θ) for each basin 9120000 9120000 !(!( !( !( Anthropic !( !(!( potential to produce large earthquakes. !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !(!(!( !( !( Mass movement !( !( !( !( !( !( !( !(!( !( !( !( 3) Calculate the χ coordinates !( !( !( !(!(!( !( Figure 1. General geomorphological units of the study area. Hillshaded digital elevation model !( !( !( !( !( !( !( !( !( !( !(!( Marine terrace !(!( !( !( !(!( !( DEMNAS 8 m resolution (http://tides.big.go.id/DEMNAS/). Reference system !( !( !( !( !( !(!( !( !( !( !( !( Steep escarpment UWGS_1984_UTM_Zone_49S. Abbreviations for major cities: BT: Bantul, YGK: Yogyakarta. 4) Extract the Ksn based on the segmentation of !( !( !( !( !( !( !( !( Lithological χ-elevation profiles !( !( !( Legend !( !( !( !( !( !( !( !( !( Undefined !( !( !( !( !( - Ksn knickpoint !( !( !(!( !( !( !( !( !( !( !( !( Seismotectonic Setting Legend !( + Ksn knickpoint !( !( !( !( Tectonic !( !(!( !( !( !( !( !( !( !( !( !( !( !( !( !( Stepped knickpoint !( !( !( !( - Ksn knickpoint 9110000 9110000 Low !( !( !( !( !( !( !( !( !( Medium Ksn Channel !( !( !( + Ksn knickpoint 120° E !( !( !( !( Channel Steepnes Hydrography !(!( !( 90° E High Steepness !( !( !( !( Stepped knickpoint (a) !( !( (b) !( 440 !( !( !( 440 !( !( !( Eurasian Plate (b) Knickpoints Local relief Local relief 9105000 !( Fault inferred from Knp 9105000 Java sea 9105000 9105000 05102.5 !( 05102.5 (1 km radius) 05102.5 (1 km radius) Marine terraces Km 0 Km 0 Km 435000 450000 30° N 6° S 420000 430000 440000 450000 460000 435000 450000 Philippine A! JK Plate (B) Figure 7. Location of knickpoints in the study area categorized by their inferred cause; obtained with Figure 5. Map of spatial distribution of Ksn (channel steepness) obtained with LSDTopoTools (Mudd et al., Figure 6. Map of spatial distribution of knickpoints overlain on local relief map. Vertical-step LSDTopoTools (Mudd et al., 2018). Faults and marine terraces deduced from them are displayed. A! SM 2018). High Ksn values are indicated in red while low in yellow. This areas are in agreement with the zone knickpoints are shown by yellow dots while slope-break knickpoints in blue (when negative value) and Geological map compiled from Rahardjo et al (1995). The western part of the area is mainly covered A! SR by recent volcanic deposits (Merapi deposits) and alluvium filling the Yogyakarta basin. The eastern BD of high hillslope gradients and local relief. red (when positive value). 0° Sunda A! part consists of Eocene-Miocene fluvial, volcanic and shallow marine sedimentary rocks. Fm. Kepek: YGK tuff and limestones. Fm. Wonosari: limestones. Fm. Oyo: tuffaceous sandstone and limestone. Fm. A! Sambipitu: calcareous sandstones. Fm. Nglanggran, Semilir and Kebo-Butak (volcanic deposits): andesitic breccias, lapilli, ruff, sandstones, shales. Basements is composed of metamorphic rocks. Indo-Australian Plate (Fig. 1) 30° S Discussion: Causative fault of Yogyakarta earthquake? Conclusions Magnitude Mw ( 4 - 4.5 4.5 - 5 424000 439500 455000 435000 450000 5 - 5.5 10°S (! The topography expressed as the Baturagung Range represent recent faulting. It is unclear 70 mm/yr (A) (B) Legend (! Active faults 5.5 - 7 (! Subduction zone ( Legend Fault inferred from Knp which of these structures are active as short-term (Quaternary to Holocene) tectonic A! Major cities Lineations inferred Transform fault SUNDA TRENCH 9135000 9135000 Depth (Km) Indian ocean ( Fault inferred from Knp from R. Sensing (! Local Magnitude Ridge Area of study (! evidence in the landforms is lacking or not yet observed, partly because the Batuarung 0 50 100 200 Lineations inferred (! -0.4 - 0.8 (! (! 0 50 125 650 (! Km ( from R. Sensing (! 0.8 - 1.4 (! Range and Sewu karst region consists of an insignificant amount of Quaternary deposits. (! 1.4 - 2.2 A (! (! Oyo river (! (!(! 108°E 112°E (! (!(!(! (! 10 (! 2.2 - 3.6 (! (!(!(! (! (!(! (! (! Other interesting feature is the Oyo river, its drainage pattern changes along its course (!(! Stress tensor (!! (! (! ! 9139500 Figure 2. a) Simplified tectonic setting of the Indonesian region. (b) Instrumental seismicityity of Java Island between 2008-201820 (USGS seismic catalogue, https://earthquake.usgs.gov). 9139500 (! (! (!(!( (! ( (! (! (! (!(!(!(! (! (! (! (!(!(!(!(!(! (! (!(! northwards and southwards at various locations suggesting that several NE-SW to N-S Thrust (! (! (! (!(! (! (! (!(! Motion of the Australian Plate at a rate of 70 mm/yr towards the Sunda Plate is indicatedd by a red arrow ((BockBock et al., 2003). Active faults are indicated by grey lines (Marliyani, 2016). (! (! (!(!(!(! (! (! (! (! (!(! (!(!(!(!(!(! Normal fault (! (! (! (!(!(! (! Abbreviations for major cities: JK: Jakarta, BD: Bandul, YGK: Yogyakarta, SR: Subraya,, SM: Semarang. (! (! (! (!(! (!(! trending faults may have controlled the drainage evolution. (! (! (! Strike-slip fault (! (! (!(!(! (!(!(! (!(! (! (! (! (! (! (!(!(!(!(!(!(!(!(!(!(!(!(! (! (! (! (!(! (!(! (!(!(! (! 420000 435000 450000 (!(! (!(!(!(!(! (!(!(! (! (! (! (! (! (!(! (! (!(! (!(!(! (! (! (! (! !(! !( (!(! (! (! (! (! (! (!((!(!(!(!(! (!(! (!(!(!!(!(! (! (! (!(!(!(!(! (!(!(! (! (!((!(!(! (! (! (!(!(!(!(!(!(!(!(!(!(!(!(!(!(! (!(!(!(! (! (! (! (! (! (! (!(!(!(!(! (!(! (!(! We are planning to conduct a field work campaign in June 2019 to solve the current (! (! (!(!(!(!(!(!(!(!! (! (!(!(! (!(! (! ( (! (! (!(! (! (!(!(!(!(!(! (! (! (! (! (!(!(! (!(!(!(!(! (!(! (!(! (! (! (!(! (! ! (!(! (! (C) (!(! (! (!(! (!(!( (! (!(! (!(!(! (!(! uncertainities. A detailed geological map will be carried out in order to find indices of active Source Parameters from USGS (! (! (! (!(! (! (!(!(! (! (!(! (! (!(! (!(!(!(!(!(! !( (!(! Java forms part of the volcanic arc in the Sunda (USA) (!(!(! (! (!(!(!(!(!(!(! (!( (! (! (!(!(! (!(!(!(!(!(!(!(! (!(!(! (! (!(! (! (!(!(!(!(! (!(! faulting and suitable sites for a paleoseismological studies, as well to corroborate the (! (! (!(!(!(!(!(!(!(! (! (! (! (!(! (! 9120000 (! (! 9120000 Magnitude (Mw) 6.3 (! (! (!(! (!(! (!(!!(!(!(!(!(! (! (! (! ! (! (! (!(!! (!(!(!(!((!(!(!(! (! (! Plate adjacent to the Java trench where the (! (!( (!(!(!((! (! (! Depth (km) 10 ! (! (!(! (! (! obtained knickpoints. To obtain better resolution data to do our surface and subsurface ( (! (! (! (!(! (!!(! (! (! (! (! (! !((! (! (! (!(!(! (! (!(!(!(!(!(! (! B Australian