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, () (1) Neotectonics and Natural Hazards, RWTH Aachen University, Aachen, Germany (2) Geological Engineering Department, Universitas Gadjah Mada, , 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 !( !( !( !( !( 4) Extract the Ksn based on the segmentation of !(!( !( !( !( !( !( Steep escarpment UWGS_1984_UTM_Zone_49S. Abbreviations for major cities: BT: Bantul, YGK: Yogyakarta. !( !( !( !( χ-elevation profiles !( !( !( !( Lithological !( !( !( 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 0 0 Km 6° S Km Km 435000 450000 30° N 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. SM A! 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 10°S 5 - 5.5 (! 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! Lineations inferred

Transform fault Major cities 9135000 9135000 Depth (Km) Indian ocean SUNDA TRENCH ( 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: , 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 (! (! (! (!(!(!(!(!(!(!(! (! (! (! (!(! (! Magnitude (Mw) 6.3 9120000 (!(! (!(! (!(! !(! (!(!(!(!(!(! 9120000 (! (! (! (!(! (!(!(! (!(!(!(! (! (! 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 750 (! (!(! (!(!(!(!(! (! Australian Plate is subducted at a rate of 71 mm/y in (! (!(! (!(!(! analysis we will perform some geophysics: GPR, ERT and drone flying. aftershock.The (! (! (! (! (! (! (! (! (!(! (! (! (! (!(!(! Aftershocks largest one (! (!(! (!(! (! (! (! a N20ºE direction according to NUVEL-1A model (! (!!( (!(! with magnitude (! (! (! (! (! ( (! 9124000 (! 9124000 shorteningshortening (! Mw 5.2 (!(! (! (! (! (Bock et al., 2003) (Figure 2). (! (! (! (!(! (! (! !(!(! (!(! (!(!(!(! (! (! ( (!(! Left-lateral (! (! (!(! (! (!(!(!(! (! (! (!(! (! (! (!(! (!(! (! Kilometers Focal strike-slip ^_ (!(! (!(!(!(! (!(!(!(!(! (! (! (!(! (! 01.25 2.5 5 Mechanism trending NE- (! (! (!(! (! (! (! (!(! (!(! 9140000 SW (! (! (! (!(!(! Yogyakarta area has experienced several NIED (! (! (!(!(!(!(! 435000 450000 (! (! (! (!(!(! (!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(! (!(!(! (! (!(! (!(! (!(! (! (! (!(!(!(!(!(!(! (!(! (! (! (! (!(! (! (!(! (! (! (! (!(! (! (! earthquake events during the time. On the 27th of 9125000 (!(! (! (!(!(!(! (!(!(!(! (! (! (!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(! (! !( (! (!!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(! (!(!(!(!(! (! extensionextension A 10 (! (! (!(!(!(!(!(!(!(!(!(!(! (!(! (!(!(! B May 2006, a M 6.3 earthquake (Figure 3) occurred in (! (!(!(!(! (!(!(!(!(!(!(!(!(!(! (! (Km) 0 (! (!(!(! (! (! (! (!(!(! (!(!(!(!(!(!(!(!(! (! 77° (!(! (! (! (! (! (!(!(!(! (! (!(!(! (C) (! (!(!(! (!(! (! (!(!(!(! (!(! (! (!(! (!(!(! the area, causing more than 6000 fatalities and $3 (!! (!(! (!(! (!(!(!(! (!(!(! (! (! ((! (! (! ((!(!(! (!(! (! (! (! (!(!!((!(!(! (!(! (! (! (!(! (!(!(!(!(!(! (!(! (!(! (! (!(!(! (! (! (! (! (! 9130000 billion economic loss. Opak Fault was initially (! (! (! (!(!(! (!(! (! (! (! (! (!(!^_ (! (!(!(! (!(!(! (!(! (! (!(!(!(!(!(!(!(! (! (! (! (!(!(!(!(! (!(!(! (!(!(!(!!( (! (! thought to be the source of this earthquake, but the (!(! (! (! (! (! (!(!(! (! (! (! (!(!(!(!(! (! (!(!(! (! USGS (! (!(! (! (! (! 9108500 (! (! (! (! (! (!(!(!(!(!(!(!(! (! 9108500 epicenter and aftershocks distributions were (! (!(!(! (! (!(!(! (! (! (!(!(! (!(! !( (! (! (! (!(!(! (! Km (! (! (! inconsistent with the extent of the fault presented at ^_ (!(! (! ^_ 05102.5 the regional geology map and the aftershock (! ESDM ERI 424000 439500 455000 9120000 distribution. ^_ ^_ Figure 9. Summary map compiling the ^_ ^_ −10 BMG CMT Figure 8. A) Map illustrating the fault system and the stress regime of the area derived from mapped features. Faults inferred from the Figure 3. Distribution of the aftershocks sequence and source parameters EMSC GEOFON earthquake focal mechanism from the World Stress Map (Heidbach et al., 2018). We interpretate knickpoint distribution and lineations by of the 2006 Yogyakarta Earthquake. Hillshaded digital elevation model 9110000 Legend remote sensing lineament analysis. Note Legend the slip tendency of the mapped faults if reactivated according to the stress regime. Note that the that not all high ksn values obtained are DEMNAS 8 m resolution (http://tides.big.go.id/DEMNAS/). Reference area experiencing more uplift is the north-east part of the Batuarung Range (thrust with nord Fault inferred from Knp considered as a fault since other 9110000 system UWGS_1984_UTM_Zone_49S. Aftershock catalogue from ^_ Epicenter by Institution Figure 4. A) Flowchart of the LSDTopoTools knickpoint detection algorithm. Simplified direction) which may be correlated by the pattern of the Oyo river flowing in this area north to Mw processes (difference in rock resistance, Lineations inferred from R. Sensing Anggraini (2013). Source parameters from USGS seismic catalogue (! Aftershocks (Anggraini, 2013) from Gailleton et al. (2018). B) Type of Knickpoints: vertical-step knickpoints and south. B) Distribution of the aftershock sequence (Anggraini, 2013) in the context of the mapped etc.) have to be taken into account. Escarpment (https://earthquake.usgs.gov). slope-break knickpoints, here illustrated both in terms of channel profile form (upper) and faults. C) Vertical section perpendicular on strike of major fault (NE-SW) of the aftershocks and Hillshaded digital elevation model Faults geological map 2 4 6 DEMNAS 8 m resolution Kilometers Marine terraces (Rahardjo et al., 1995) 05102.5 slope-area relations (bottom) (Whipple et al., 2013). C) Example of knickpoint extraction main shock (in red). 05102.5 Km for a basin of the study area shown for the channel long profiles. (http://tides.big.go.id/DEMNAS/). 420000 430000 440000 450000 460000

References Sara Pena-Castellnou, Ms.C. Heidbach, O., et al., 2018. The World Stress Map database release 2016: Crustal stress pattern across scales. Tectonophysics 744, 484–498. https://doi.org/10.1016/j.tecto.2018.07.007 Rahardjo, W., Sukandarrumidi, Rosidi, H., 1995. Peta Geologi Lembar Yogyakarta, Jawa (Yogyakarta Quadrangle Geological Map). Anggraini, A., 2013. The 26 May 2006 yogyakarta earthquake, aftershocks and interactions. Universität Potsdam. Marliyani, G.I., 2016. Crustal Deformation in the Overriding Plate of an Orthogonal Subduction System. Arizona State University. Setijadji, L.D., et al., 2006. Searching for the Active Fault of the Yogyakarta Earthquake of 2006 Using Data Integration on Aftershocks , Cenozoic Geo- History , and Tectonic Geomorphology, in: Bock, Y., et al., 2003. Crustal motion in Indonesia from Global Positioning System measurements. J. Geophys. Res. 108, 2367. https://doi.org/10.1029/2001JB000324 Karnawati, D., Pramumijoyo, S., Anderson, R., Husein, S. (Eds.), May 27, 2006The Yogyakarta Earthquake Of. Star Publishing Company, pp. 1–23. Tel: +49 (0) 241 80 98906 Marliyani, G.I., et al. 2016. Characterization of slow slip rate faults in humid areas: Cimandiri fault zone, Indonesia. J. Geophys. Res. Earth Surf. 121, 1–22. https://doi.org/10.1002/2016JF003846 Gailleton, B., et al., 2019. A segmentation approach for the reproducible extraction and quantification of knickpoints from river long profiles. Earth Surf. Dyn. 7, 211–230. , E-Mail: [email protected] https://doi.org/10.5194/esurf-7-211-2019 Mudd, S.M., et al., 2018. The LSDTopoTools Chi Mapping Package. https://doi.org/10.5281/zenodo.1291889 Whipple, K.X., et al., 2013. Bedrock Rivers, Treatise on Geomorphology. Elsevier Ltd. https://doi.org/10.1016/B978-0-12-374739-6.00254-2