Palu-Koro Fault Research Articles

Resistivity model of hallow subsurface to find the path of geothermal manifestation in Bora Village of Sigi Regency of Central Sulawesi

Bora geothermal is one of the manifestations that appear at the meeting of two fault zones namely Palu-Koro Fault and Palolo Fault. This geothermal is classified as non-volcanic. Existing tectonic activity, presumably leading to the formation of a depressive zone that triggers a rock intrusion process that conducts heat conductively. To find out the sub-surface structure, we apply the electrical resistivity tomography (ERT) method. The data collection technique we use is 2-D imaging with Wenner configuration, where the number of electrodes is 21 pieces at 6 m intervals. Shallow depths Penetration targeted about 20 m below ground surface (m.bgs. The resistivity values obtained are in the range < 0.15 Ohm.m to > 56.6 Ohm.m which indicates the subsurface layer is strongly influenced by the fluid. However, the interesting thing here is that the hot water pool formed on the surface of about 6 m dimension is passed through the path of ERT measurement around the electrode number 11 and 12, illustrated in the resistivty section to ± 10 m.bgs depth and turning toward the electrode number 4 up to 7 as the lowest anomaly source at depth > 15 m.bgs. This configuration of low resistivity anomaly is what we interpret as a shallow ground pathway with local high temperatures as the source of the emergence of Bora geothermal manifestations.

Geodetic Observations of the 2018 Mw 7.5 Sulawesi Earthquake and Its Implications for the Kinematics of the Palu Fault

AbstractThe ascending and descending interferometric synthetic aperture radar data are used to investigate the fault rupture and slip model of the 2018 Mw 7.5 Sulawesi, Indonesia, earthquake. The best fitting slip model indicates that this earthquake ruptured not only a segment extending the Palu fault to the north but also a northwestern segment offshore. The slip on the onshore fault is predominant left‐lateral strike slip. The slip on the offshore fault is dominated by normal faulting with a maximum slip of ~6.3 m. The newly discovered offshore normal faulting is likely to be the cause of the tsunami after the shock. Combined with previous geomorphic, tectonic, geodetic, and modeling studies, we suggest that the kinematics of the Palu fault maintained the same style of faulting from north to south, which resulted from an oblique extension occurred on an east dipping fault at depths. The deformation pattern of NW Sulawesi is dominated by this slip mechanism.

Determination of temporal value of a-value and b-value to identify the level brittle of rock and seismic activity in the Palu region

&lt;span lang="EN-US"&gt;The Palu area is a region that has a high seismic potential as a result of the existence of the Palu Koro Fault. The Koro Palu Fault is an active sinistral fault that moves with velocity around 25-30 mm/year. This research purpose to determine the a-value and b-value temporally for identify rock brittle levels and seismicity levels in the Palu area using the Maximum Likelihood Guttenberg-Richter method. The data used in this study are earthquake data from the BMKG and USGS catalogs for 2008-2018 over a period of 10 years located at 0840 LU 40 2.620LS and 118,590 BT - 121.70 BT. Based on the results of data processing, there were 3033 earthquake distributions in the earthquake over a 10-year period. The calculation results show variations in the value of b-values in the range 0.55-0.961 and the a-value in the range 3.63-5.42. The highest b-value was obtained in 2015 at 0.961 as an indication of increased seismic activity in the Palu area. After the Palu M 7.4 earthquake on 28 September 2018, there was a significant decrease in the value of the b-value to 0.685. Based on the trend of b-value values which continued to decline from 2015 until 2018, it was identified in the rock's resistance to stress is high in the Palu area. Whereas for the seismicity index value of the Palu area of 0.040789 with the earthquake return period 7 is 25 years. &lt;/span&gt;

Evidence of supershear during the 2018 magnitude 7.5 Palu earthquake from space geodesy

A magnitude 7.5 earthquake hit the city of Palu in Sulawesi, Indonesia on 28 September 2018 at 10:02:43 (coordinated universal time). It was followed a few minutes later by a 4–7-m-high tsunami. Palu is situated in a narrow pull-apart basin surrounded by high mountains of up to 2,000 m altitude. This morphology has been created by a releasing bend in the Palu-Koro fault, a rapidly moving left-lateral strike-slip fault. Here we present observations derived from optical and radar satellite imagery that constrain the ground surface displacements associated with the earthquake in great detail. Mapping of the main rupture and associated secondary structures shows that the slip initiated on a structurally complex and previously unknown fault to the north, extended southwards over 180 km and passed through two major releasing bends. The 30 km section of the rupture south of Palu city is extremely linear, and slightly offset from the mapped geological fault at the surface. This part of the rupture accommodates a large and smooth surface slip of 4–7 m, with no shallow slip deficit. Almost no aftershock seismicity was recorded from this section of the fault. As these characteristics are similar to those from known supershear segments, we conclude that the Palu earthquake probably ruptured this segment at supershear velocities. The devastating 2018 magnitude 7.5 earthquake in Palu, Indonesia, ruptured at supershear speeds according to evidence from space geodesy.

Walanae Fault Kinematic Deduced from Geometric Geodetic GNSS GPS Monitoring

The western Sulawesi region has the main structural boundary, the Palu Koro Fault which divides from Palu Bay at the northest part to Central Sulawesi and continues into the Bone Gulf in southest part. In the southern part of this region, namely the South Sulawesi Arm zone, there is a Walanae fault which is defined as a sinistral wrench with a NW-SE direction that divides the South Arm of Sulawesi. This fault in the northern part is expected to continue to the northwest intersecting the Makassar Strait and unite with Paternoster-Lupar (Kalimantan) sutures and at the southest ending in Flores thrust fault. Walanae fault system did not only have one strand but was divided into 4 parts, namely the northern East Walanae Fault with a slip rate of 6.634 mm/year and the southern part with a 7.097 mm/year of slip rate, as well as the northern part of West Walanae Fault with a slip rate of 4.528 mm/year and the southern part with a slip rate of 3.270 mm/year. The northern part of Walanae fault system has opening or spreading pattern occurs that is in harmony with the formation of Walanae depression. By using simple geometric modeling, we found the fault system have 2 strain partitions with dominant sinistral strike slip pattern at southern part and combination between left lateral strike slip with thrust fault pattern at northern part.

A Block Ramp Errors Correction Method of Planet Subpixel Offset: Application to the 2018 Mw 7.5 Palu Earthquake, Indonesia

Planet optical images have a short revisit period and high spatial resolution, so they have great potential in surface offset monitoring. However, few studies have focused on the error source analysis and accuracy improvement in the offset field of Planet images. In this study, we investigate the optimal band selection of the Planet images and the error sources for subpixel offset monitoring, using the 28 Sept. 2018 Mw7.5 Palu earthquake as an example. The results show that Band 2 is the optimal band for surface offset monitoring and ramp errors are the dominating error source in the offset field. Considering the imaging characteristics of Planet satellites, we propose a block ramp errors correction method. Our proposed method can improve the accuracy of the Planet subpixel offset by 25% in comparison with the traditional method. We also compare the Planet images subpixel offset result with the Sentinel-2 subpixel offset result and find they are in good consistency. We combine the corrected Planet images offset and SAR images offset to solve the complete 3D deformation field of the Palu earthquake, which shows that the ruptured fault is a left-lateral strike-slip fault accommodated with normal component in the Palu-Koro fault. The earthquake was dominated by south-north and vertical deformation, with the maximum deformation of 6 m and 4 m in the horizontal and vertical directions, respectively. This study also has set a good example for using the Planet images for natural hazards monitoring (such as earthquakes and landslides).

Analysis of Focal Mechanism Distribution in Northern Sulawesi

Sulawesi has been known to have the complex condition of the geology and tectonics. It is indicated by natural phenomena such as volcanoes and earthquakes in Sulawesi. This study aimed to determine the latest tectonic order in Sulawesi based on the distribution focal mechanism. The locations of the study were in the Sulawesi 2º22’ N – 3º48’ S and 119º22’ – 124º22’. The earthquake data used were from BMKG since 2001 to 2015 with the criteria > M4.5. The strike, dip, and rake data were through Global-CMT for the earthquake in Sulawesi at the same time. An AB cross-section lies along the neck of Sulawesi which has strike-slip fault type of focal mechanism with a shallow depth allegedly caused by Palu Koro Fault activity. CD longitudinal section elongated in the eastern arm of Sulawesi to the ocean, which is dominated by the strike-slip fault showing the activity of Batui Fault at the shallow depths. Matano Fault activity was observed in EF cross-section dominated by a strike-slip fault on the land and at sea by a normal fault. This activity was observed at the shallow depths which shows Matano Fault activity. GH cross section was an event with depth with various subtypes of reverse fault which is relatively uniform turning into an indication of the Sulawesi Sea subduction activity.

Seismicity of Batubesi Dam at Sorowako Region Based on Earthquake Data and Microtremor Measurement

Batubesi Dam which is located in Sorowako region in the middle part of Sulawesi island had been designed with seismic coefficient about 0.20g. The region constitutes an active earthquake zone with the recurrence frequency and magnitude of the earthquake are relatively high. The region is located on and active fault zone due to lateral fault movement (strike-slip) of Matano fault, Palukoro fault, and Walanea fault that categorized as shallow crustal earthquakes. To recognize characteristic of the earthquake at the site of interest, the historical earthquakes (background) data surrounding the study area and local microtremor measurements data are analyzed by means of a probabilistic seismic hazard analysis (PSHA) and deterministic seismic hazard analysis (DSHA) using some ground-motion models in attenuation relationship equations in resulting of seismic hazard parameter as represented by peak ground acceleration (PGA) values in earthquake scenario at operating basis earthquake (OBE), maximum design earthquake (MDE), and maximum credible earthquake (MCE) conditions. The PGA value in OBE condition is about 0.35g, in MDE about 0.45g, and in MCE about 0.49g. These values are used as reference to evaluate compliance of the current technical aspects with the new required design facing the updated seismicity parameters.

Earthquake Hazard Analysis Use Vs30 Data In Palu

Palu City is an area passed by Palu-Koro fault and some small faults around it, causing the Palu of city often hit by earthquake. Therefore, this study is intended to mapped the earthquake hazard zones. Determination of this zone is one of aspect that can be used to reducing risk of earthquake disaster. This research was conducted by integrating Vs30 data from USGS with Vs30 from mikrotremor data. Vs30 data from microtremor used to correction Vs30 from USGS. This Results are then used to determine PeakGround Acceleration (PGA) can be used to calculate the impact of earthquake disaster. Results of the study shows that Palu City is in high danger class. Eight sub-districts in Palu City, there are 7 sub-districts that have high danger level, namely Palu Barat, PaluTimur, Palu Selatan, Palu Utara, Tatanga, Mantikulore and Tawaeli.

Rapid cooling and exhumation as a consequence of extension and crustal thinning: Inferences from the Late Miocene to Pliocene Palu Metamorphic Complex, Sulawesi, Indonesia

Metamorphic complexes forming high mountains of 1.5–2km in Western Sulawesi were previously considered to be Mesozoic or older basement of Gondwana crust. However, many of the metamorphic rocks are much younger than previously thought. Some have Eocene sedimentary protoliths. New geothermobarometric and geochronological data from metamorphic rocks of the Palu Metamorphic Complex (PMC) and associated granitoids provide information on the timing and mechanisms of Neogene metamorphism and contemporaneous rapid exhumation. The metamorphic rocks are strongly deformed and some were partially melted to form migmatites. Schists contain relict andalusite, cordierite, staurolite and Mn-rich garnet which are wrapped by a pervasive fabric. 40Ar/39Ar dating of biotite, white mica and amphibole from strongly deformed, mylonitic schists and recrystallised amphibolites reveals cooling occurred in the Early Pliocene (c. 5.3–4.8Ma) in the northern part and during the Late Pliocene (c. 3.1–2.7Ma) in the southern part of the PMC. U-Pb, 40Ar/39Ar and (U-Th)/He analyses of various minerals from PMC metamorphic and S-type magmatic rocks give very similar mid to Late Pliocene ages, indicating very fast cooling and rapid exhumation, and show the high speed at which tectonic processes, including magmatism, exhumation, and reworking into a sediment, must have occurred. The high rates could be unique to this area but we suggest they record the true speed of metamorphic complex exhumation in a very young orogenic belt. Rates in older orogens appear lower because they are averages measured over longer periods of time. Contemporaneous magmatism and deformation are interpreted as a consequence of decompressional melting due to extension and thinning of the crust, promoted by possible detachment faults and normal faulting at the major NW-trending Palu-Koro and Tambarana Faults. In contrast, I-type magmatic rocks, separated from the PMC by the Palu-Koro Fault, were exhumed from upper crustal levels by erosion at moderate rates.

Precise Hypocenter Determination around Palu Koro Fault: a Preliminary Results

Sulawesi area is located in complex tectonic pattern. High seismicity activity in the middle of Sulawesi is related to Palu Koro fault (PKF). In this study, we determined precise hypocenter around PKF by applying double-difference method. We attempt to investigate of the seismicity rate, geometry of the fault and distribution of focus depth around PKF. We first re-pick P-and S-wave arrival time of the PKF events to determine the initial hypocenter location using Hypoellipse method through updated 1-D seismic velocity. Later on, we relocated the earthquake event using double-difference method. Our preliminary results show the distribution of relocated events are located around PKF and have smaller residual time than the initial location. We will enhance the hypocenter location through updating of arrival time by applying waveform cross correlation method as input for double-difference relocation.

Fault systems of the eastern Indonesian triple junction: evaluation of Quaternary activity and implications for seismic hazards

Abstract Eastern Indonesia is the site of intense deformation related to convergence between Australia, Eurasia, the Pacific and the Philippine Sea Plate. Our analysis of the tectonic geomorphology, drainage patterns, exhumed faults and historical seismicity in this region has highlighted faults that have been active during the Quaternary (Pleistocene to present day), even if instrumental records suggest that some are presently inactive. Of the 27 largely onshore fault systems studied, 11 showed evidence of a maximal tectonic rate and a further five showed evidence of rapid tectonic activity. Three faults indicating a slow to minimal tectonic rate nonetheless showed indications of Quaternary activity and may simply have long interseismic periods. Although most studied fault systems are highly segmented, many are linked by narrow (&lt;3 km) step-overs to form one or more long, quasi-continuous segment capable of producing M&gt;7.5 earthquakes. Sinistral shear across the soft-linked Yapen and Tarera–Aiduna faults and their continuation into the transpressive Seram fold–thrust belt represents perhaps the most active belt of deformation and hence the greatest seismic hazard in the region. However, the Palu–Koro Fault, which is long, straight and capable of generating super-shear ruptures, is considered to represent the greatest seismic risk of all the faults evaluated in this region in view of important strike-slip strands that appear to traverse the thick Quaternary basin-fill below Palu city.

DETERMINED SOIL CHARACTERISTIC OF PALU IN INDONESIA BY USING MICROTREMOR OBSERVATION

The Palu city, which is located in the active seismic zone of the Palu-Koro fault. Several powerful earthquakes have struck Palu city at previous years. One of the greatest earthquake event occurred in year 2006 which 6.2 Mw, about more a hundred buildings and houses were collapsed due to this earthquake. Palu-Koro fault also produced several tsunami events in year of 1927, 1968 and 1996. The latest earthquake struck Palu on 2012 (7.2 Mw) and it produced local tsunami. Since no soil profile map of Palu region available, we performed single observations of microtremors at 122 sites in Palu. Its results enabled us to estimate the site dependent amplification characteristics of earthquake ground-motion. We also conducted a 8-site microtremor array investigation to gain a representative determination of the soil condition of subsurface structures in Palu. From the dispersion curve of array observations, the central business district of Palu corresponds to relatively from soft soil to medium condition. Predominant periods due to horizontal vertical ratios (HVSRs) in Palu are in the range of 1.2 to 2.5 s

The Palu Metamorphic Complex, NW Sulawesi, Indonesia: Origin and evolution of a young metamorphic terrane with links to Gondwana and Sundaland

The Palu Metamorphic Complex (PMC) is exposed in a late Cenozoic orogenic belt in NW Sulawesi, Indonesia. It is a composite terrane comprising a gneiss unit of Gondwana origin, a schist unit composed of meta-sediments deposited along the SE Sundaland margin in the Late Cretaceous and Early Tertiary, and one or more slivers of amphibolite with oceanic crust characteristics. The gneiss unit forms part of the West Sulawesi block underlying the northern and central sections of the Western Sulawesi Province. The presence of Late Triassic granitoids and recycled Proterozoic zircons in this unit combined with its isotopic signature suggests that the West Sulawesi block has its origin in the New Guinea margin from which it rifted in the late Mesozoic. It docked with Sundaland sometime during the Late Cretaceous. U–Th–Pb dating results for monazite suggest that another continental fragment may have collided with the Sundaland margin in the earliest Miocene. High-pressure (HP) and ultrahigh-pressure (UHP) rocks (granulite, peridotite, eclogite) are found as tectonic slices within the PMC, mostly along the Palu–Koro Fault Zone, a major strike-slip fault that cuts the complex. Mineralogical and textural features suggest that some of these rocks resided at depths of 60–120km during a part of their histories.Thermochronological data (U–Th–Pb zircon and 40Ar/39Ar) from the metamorphic rocks indicate a latest Miocene to mid-Pliocene metamorphic event, which was accompanied by widespread granitoid magmatism and took place in an extensional tectonic setting. It caused recrystallization of, and new overgrowths on, pre-existing zircon crystals, and produced andalusite–cordierite–sillimanite–staurolite assemblages in pelitic protoliths, indicating HT–LP (Buchan-type) metamorphism. The PMC was exhumed as a core complex at moderate rates (c. 0.7–1.0mm/yr) accompanied by rapid cooling in the Plio-Pleistocene. Some of the UHP rocks were transported to the surface at significantly higher rates (⩾16mm/yr).The results of our study do not support recent plate tectonic reconstructions that propose a NW Australia margin origin for the West Sulawesi block (e.g. Hall et al., 2009).

ESTIMATION OF SUBSURFACE STRUCTURE BASED ON MICROTREMOR, BORE HOLE OBSERVATIONS AND STOCHASTIC STRONG GROUND MOTION SIMULATIONS IN PALU CITY, CENTRAL SULAWESI, INDONESIA: A VALIDATION AND SENSITIVITY STUDY ON THE 23 JANUARY 2005 (PALU) EARTHQUAKE

In this study, we investigated the subsurface structure and strong ground motion parameters for Palu City. One of the major structures in Central Sulawesi is the Palu-Koro Fault system. Several powerful earthquakes have struck along the Palu-Koro Fault during recent years, one of the largest of which was an M 6.3 event that occurred on January 23, 2005 and caused several casualties. Following the event, we conducted a microtremor survey to estimate the shaking intensity distribution during the earthquake. From this survey we produced a map of the peak ground acceleration, velocity and ground shear strain in Palu City. We performed single observations of microtremors at 151 sites in Palu City. The results enabled us to estimate the site-dependent shaking characteristics of earthquake ground motion. We also conducted 8-site microtremor array investigation to gain a representative determination of the soil condition of subsurface structures in Palu. From the dispersion curve of array observations, the central business district of Palu corresponds to relatively soil condition with Vs ≤ 300 m/s, the predominant periods due to horizontal vertical ratios (HVSRs) are in the range of 0.4 to 1.8 s and the resonant frequency are in the range of 0.7 to 3.3 Hz. Three boreholes were throughout the basin especially in Palu area to evaluate the geotechnical properties of subsurface soil layers. The depths are varying from 1 m to 30 m. Strong ground motions of the Palu area were predicted based on the empirical stochastic green’s function method. Peak ground acceleration and peak ground velocity becomes more than 0.04 g and 30 kine in some areas, which causes severe damage for buildings in high probability. Keywords: Palu-Koro fault, microtremor, bore holes, peak ground acceleration and velocity.

SITE RESPONSE CHARACTERISTICS OF H/V SPECTRUM BY MICROTREMOR SINGLE STATION OBSERVATIONS AT PALU CITY, INDONESIA

In this study, we estimated predominant period of an H/V spectrum in Palu City, Indonesia, by using microtremor single station observations. Sulawesi Island, eastern Indonesia, is located at the junction between the converging Pacific-Philippine, Indo- Australian Plates and the Eurasian Plate. One of the major structures in Central Sulawesi is the Palu- Koro Fault system, which extends NNW-SSE direction and cross-cuts Sulawesi along more than 300 km from the North Sulawesi trench passing southward through Palu Bay then turn to the southeast, connecting to the Matano and Lawanopo Faults and further eastward both faults join to Tolo trench. Several earthquakes have been known along Palu-Koro Fault system such as Gimpu earthquake (1905), Kulawi earthquake (1907), Kantewu earthquake (1934), and offshore Donggala earthquake (1968) which caused tsunami that destroyed 800 houses and killed 200 people at Donggala district. Palu City, located at the northern tip of Palu depression, is a capital of the Central Sulawesi Province. It is located in the active seismic zone of the Palu-Koro fault. Spectral ratios for horizontal and vertical motion (H/V) from single-station microtremor records were used to identify the predominant periods of the ground vi- brations. Understanding the parameters of predominant period[s] and seismichazard is important for mitigation and environmental planning of the Palu region. Keywords: H/V spectrum, predominant period[s], microtremor single station observation

Ductile flow in the metamorphic rocks of central Sulawesi

Abstract Metamorphic rocks exposed along the Palu-Koro Fault of west-central Sulawesi, Indonesia, show abundant evidence of non-coaxial ductile deformation. The deformed rocks include gneisses, amphibolites and schists, that form part of a regionally metamorphosed basement complex of Mesozoic–Precambrian Australian (Gondwanan) origin. In the Palu and Neck regions of Sulawesi, ductile shear fabrics record low-angle westward extension. Further south in the Palu valley, extension is directed towards the south and SW, along with gently-dipping ductile thrust fabrics. Vergence exceptions are common at both outcrop and kilometre scale. Cross-cutting granitic dykes place some constraint on the timing of ductile foliation formation. In the neck region of Sulawesi, it occurred before c . 44–33.7 Ma. In the central and northern Palu valley, to the south, it occurred before 5–3.5 Ma. The timing and orientation of non-coaxial strain precludes its origin as a result of Palu-Koro Fault activity. Instead, ductile flow occurred during either Eocene–Miocene mid-crustal extension above a metamorphic core complex, Cretaceous subduction-related deformation in the over-riding plate, or intracontinental deformation within Gondwana.

Present-day stress and deformation field within the Sulawesi Island area (Indonesia) : geodynamic implications

Present-day stress and deformation field within the Sulawesi Island area (Indonesia) : geodynamic implications

Migration of seismicity and earthquake interactions monitored by GPS in SE Asia triple junction: Sulawesi, Indonesia

Global Positioning System (GPS) measurements made in Sulawesi, Indonesia, from 1992 to 1999 detected coseismic and transient postseismic deformation related to the 1 January 1996, Mw = 7.9 earthquake on the North Sulawesi (Minahassa) trench. These motions are superimposed on the long‐term secular motion (40 mm/yr) of the left‐lateral Palu fault in central Sulawesi and continued for about 1.5–2 years. Following the earthquake, a string of earthquakes (of magnitude &gt;6) migrated along the Minahassa trench, from west to east. Subsequently, two earthquakes of magnitude &gt;6 occurred on or near the Palu fault migrating toward the south. Modeling the increase in Coulomb stress generated by the successive earthquakes agrees with the hypothesis of interacting events. An unclamping effect, possibly due to fluid migration in the Palu area, is also suggested by the stress computations and the detected (GPS) displacements.

Rapid rotations about a vertical axis in a collisional setting revealed by the Palu Fault, Sulawesi, Indonesia

Global Positioning System (GPS) measurements from 1992 to 1995 indicate that the left‐lateral Palu fault in central Sulawesi slips at a rate of 38±8 mm/a with a locking depth between 2 and 8 km. From the measured slip rate and the historic seismicity of the fault, we estimate that the Palu fault currently has stored enough strain to produce a Mw&gt;7 earthquake. The Palu and other nearby faults accommodate rapid clockwise rotation of nearly 4°/Ma of E Sulawesi relative to eastern Sunda. The rotation of east Sulawesi transfers E‐W shortening between the Pacific and Eurasian plates to N‐S subduction of the Celebes Basin beneath Sulawesi.