36 research outputs found
Recommended from our members
Crustal Deformation and Fault Strength of the Sulawesi Subduction Zone
This paper investigates the seismicity and rheology of the North-Sulawesi subduction zone. Body-wave modeling is used to estimate focal mechanisms and centroid depths of moderate magnitude (M5âM6.5) earthquakes on the North Sulawesi megathrust and surrounding region. The slip vectors of megathrust earthquakes radiate outward from Sulawesi, indicating motion that is incompatible with the relative motion of two rigid plates. Instead, the observed deformation implies lateral spreading of high topography, controlled by gravitational potential energy contrasts. This finding suggests that the observed deformation of Sulawesi results from stresses transmitted through the lithosphere, rather than basal tractions due to circulation in the mantle. Our modeling of the force balance on the megathrust shows that the subduction megathrust is weak, with an average shear stress of âŒ13 MPa and an effective coefficient of friction of 0.03. Elsewhere in Sulawesi, slip vectors of other earthquakes suggest similar potential-energy-driven deformation is present, but at significantly slower rates. Our results show the importance of lateral rheology contrasts in determining deformation rate, and hence seismic hazard, in response to a given driving force.Newton Institutional Links
Leverhulme Fellowshi
Subducted lithospheric boundary tomographically imaged beneath the arc-continent collision in eastern Indonesia
We use travelâtimes from a temporary seismic deployment of 30 broadband seismometers and a national catalog of arrival times to construct a finite frequency teleseismic Pâwave tomographic model of the upper mantle beneath eastern Indonesia, where subduction of the IndoâAustralian plate beneath the Banda Arc transitions to arcâcontinent collision. The change in tectonics is due to a change from oceanic to continental lithosphere in the lower plate as inferred from geologic mapping and geophysical, geochemical, and geodetic measurements. At this inferred transition, we seismically image the subducted continentâocean boundary at upper mantle depths that links volcanism on Flores to amagmatic orogenesis on Timor. Our tomographic images reveal a relatively high velocity feature within the upper mantle, which we interpret as the subducted IndoâAustralian slab. The slab appears continuous yet deformed as a result of the change in buoyancy due to the composition of the incoming continental lithosphere. Accordingly, there is a difference in dip angle between the oceanic and continental sections of the slab albeit not a gap or discontinuity. We suggest the slab has deformed without tearing to accommodate structural and kinematic changes across the continentâocean boundary as the two sections of the slab diverge. These results suggest that deformation in tectonic collisions can be localized along a continentâocean boundary, even at depth. We propose that future slab tearing may develop where we observe slab deformation in our study region and that a similar process may take place in collisions generally.This work was
funded by the National Science
Foundation (NSF) Grant EARâ1250214
as well as DIKTI Grant 127/SP2H/
PTNBH/DRPM/2018
Curie Point Depth Analysis of Lesugolo Area, East Nusa Tenggara, Indonesia Based on Ground Magnetic Data
The Curie point depth, or magnetic basal depth, of the Lesugolo geothermal area in Ende, Flores Island, East Nusa Tenggara, Indonesia was estimated by performing spectral analysis on spatial magnetic data and transforming it into the frequency domain, resulting in a link between the 2D spectrum of magnetic anomalies and the depths of the top and centroid of the magnetic sources. Shallow Curie point depths of 16 to 18 km were found in the north-northeast to southeast areas of Lesugolo, while deeper depths of 24 to 26 km were found in the southwest. The tectonic setting beneath the central part of Flores Island governs the distribution of the Curie point depths in the area. Shallow Curie point depth zones are associated with high thermal gradients (30 to 34 °C/km) and heat flow (80 to 100 mW/m2). Deep depths, on the other hand, correspond to zones of low thermal gradient (21 to 26 °C/km) and low heat flow (65 to 80 mW/m2). Both the derived thermal gradient and the heat flow maps contribute to a better understanding of the Lesugolo geothermal systemâs configuration. This study suggests that the Lesugolo geothermal areaâs prospect zone is located in the center of the investigated area, where the Lesugolo normal fault forms its southeastern boundary
Curie Point Depth Analysis of Lesugolo Area, East Nusa Tenggara, Indonesia Based on Ground Magnetic Data
The Curie point depth, or magnetic basal depth, of the Lesugolo geothermal area in Ende, Flores Island, East Nusa Tenggara, Indonesia was estimated by performing spectral analysis on spatial magnetic data and transforming it into the frequency domain, resulting in a link between the 2D spectrum of magnetic anomalies and the depths of the top and centroid of the magnetic sources. Shallow Curie point depths of 16 to 18 km were found in the north-northeast to southeast areas of Lesugolo, while deeper depths of 24 to 26 km were found in the southwest. The tectonic setting beneath the central part of Flores Island governs the distribution of the Curie point depths in the area. Shallow Curie point depth zones are associated with high thermal gradients (30 to 34 °C/km) and heat flow (80 to 100 mW/m2). Deep depths, on the other hand, correspond to zones of low thermal gradient (21 to 26 °C/km) and low heat flow (65 to 80 mW/m2). Both the derived thermal gradient and the heat flow maps contribute to a better understanding of the Lesugolo geothermal systemâs configuration. This study suggests that the Lesugolo geothermal areaâs prospect zone is located in the center of the investigated area, where the Lesugolo normal fault forms its southeastern boundary
Recommended from our members
SASSY21: A 3-D Seismic Structural Model of the Lithosphere and Underlying Mantle Beneath Southeast Asia From Multi-Scale Adjoint Waveform Tomography
Abstract: We present the first continentalâscale seismic model of the lithosphere and underlying mantle beneath Southeast Asia obtained from adjoint waveform tomography (often referred to as fullâwaveform inversion or FWI), using seismic data filtered at periods from 20 to 150 s. Based on >3,000 hr of analyzed waveform data gathered from âŒ13,000 unique sourceâreceiver pairs, we image isotropic Pâwave velocity, radially anisotropic Sâwave velocity and density via an iterative nonâlinear inversion that begins from a 1âD reference model. At each iteration, the full 3âD wavefield is determined through an anelastic Earth, accommodating effects of topography, bathymetry and ocean load. Our data selection aims to maximize sensitivity to deep structure by accounting for body wave arrivals separately. SASSY21, our final model after 87 iterations across seven period bands, is able to explain trueâamplitude data from events and receivers not included in the inversion. The tradeâoff between inversion parameters is estimated through an analysis of the Hessianâvector product. SASSY21 reveals detailed anomalies down to the mantle transition zone, including multiple subduction zones. The most prominent feature is the (Indoâ)Australian plate descending beneath Indonesia, which is imaged as one continuous slab along the 180° curvature of the Banda Arc. The tomography confirms the existence of a hole in the slab beneath Mount Tambora and locates a high Sâwave velocity zone beneath northern Borneo that may be associated with subduction termination in the midâlate Miocene. A previously undiscovered feature beneath the east coast of Borneo is also revealed, which may be a signature of postâsubduction processes, delamination or underthrusting from the formation of Sulawesi
Recommended from our members
Earthquake monitoring of the Baribis Fault near Jakarta, Indonesia, using borehole seismometers
Abstract: The geological setting of Jakarta and its immediate surroundings are poorly understood, yet it is one of the few places in Indonesia that is impacted by earthquakes from both the Java subduction zone and active faults on land. In this study, a borehole seismic experiment with low noise characteristics was deployed to record seismic activity on the ~ E-W oriented Baribis Fault, which is ~ 130 km long, passes to the south of Jakarta, and is only ~ 20 km away at its nearest point. A primary objective of this study is to determine whether this fault is seismically active, and therefore, whether it might pose a threat to nearby population centers, including Jakarta in particular. A total of seven broadband instruments that spanned Jakarta and the surrounding region were installed between the end of July 2019 and August 2020, during which time we were able to detect and locate 91 earthquakes. Two earthquakes were located close to the Baribis Fault line, one of which was felt in Bekasi (southeast of Jakarta) where it registered II-III on the Modified Mercalli Intensity (MMI) scale. The focal mechanism solutions of these events indicate the presence of a thrust fault, which is in good agreement with previous studies, and suggest that the Baribis Fault is active
Recommended from our members
Implications for megathrust earthquakes and tsunamis from seismic gaps south of Java Indonesia
Abstract: Relocation of earthquakes recorded by the agency for meteorology, climatology and geophysics (BMKG) in Indonesia and inversions of global positioning system (GPS) data reveal clear seismic gaps to the south of the island of Java. These gaps may be related to potential sources of future megathrust earthquakes in the region. To assess the expected inundation hazard, tsunami modeling was conducted based on several scenarios involving large tsunamigenic earthquakes generated by ruptures along segments of the megathrust south of Java. The worst-case scenario, in which the two megathrust segments spanning Java rupture simultaneously, shows that tsunami heights can reach ~ 20 m and ~ 12 m on the south coast of West and East Java, respectively, with an average maximum height of 4.5 m along the entire south coast of Java. These results support recent calls for a strengthening of the existing Indonesian Tsunami Early Warning System (InaTEWS), especially in Java, the most densely populated island in Indonesia
Implications for megathrust earthquakes and tsunamis from seismic gaps south of Java Indonesia
Relocation of earthquakes recorded by the agency for meteorology, climatology and geophysics (BMKG) in Indonesia and inversions of global positioning system (GPS) data reveal clear seismic gaps to the south of the island of Java. These gaps may be related to potential sources of future megathrust earthquakes in the region. To assess the expected inundation hazard, tsunami modeling was conducted based on several scenarios involving large tsunamigenic earthquakes generated by ruptures along segments of the megathrust south of Java. The worst-case scenario, in which the two megathrust segments spanning Java rupture simultaneously, shows that tsunami heights can reachâ~â20 m andâ~â12 m on the south coast of West and East Java, respectively, with an average maximum height of 4.5 m along the entire south coast of Java. These results support recent calls for a strengthening of the existing Indonesian Tsunami Early Warning System (InaTEWS), especially in Java, the most densely populated island in Indonesia
Recommended from our members
Foreshockâmainshockâaftershock sequence analysis of the 14 January 2021 (Mw 6.2) MamujuâMajene (West Sulawesi, Indonesia) earthquake
AbstractWe present here an analysis of the destructive Mw 6.2 earthquake sequence that took place on 14 January 2021 in MamujuâMajene, West Sulawesi, Indonesia. Our relocated foreshocks, mainshock, and aftershocks and their focal mechanisms show that they occurred on two different fault planes, in which the foreshock perturbed the stress state of a nearby fault segment, causing the fault plane to subsequently rupture. The mainshock had relatively few aftershocks, an observation that is likely related to the kinematics of the fault rupture, which is relatively small in size and of short duration, thus indicating a high stress-drop earthquake rupture. The Coulomb stress change shows that areas to the northwest and southeast of the mainshock have increased stress, consistent with the observation that most aftershocks are in the northwest.</jats:p