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Crustal movement and faults in the Banda inner and outer arcs a, GPS observations of crustal motion along an idealized profile through the Banda inner and outer arcs. Supplementary Fig. 1 shows the locations of GPS measurement sites BAPI, BANI, CUAL and CSAU (note that vertical motions are not available for BAPI, and residual horizontal motions for CUAL and CSAU are not shown because their horizontal velocities were used in the block modelling). Residual horizontal velocities at BAPI and BANI and vertical velocities at BANI in the Banda Islands are compared with modelled velocities⁴² for interseismic locking of a shallow-dip (12°) normal fault slipping at 5 cm yr–1. Vertical motions at CUAL and CSAU are also indicated as possibly due to locking of faults in the Tanimbar–Seram fold-and-thrust belt. b, A conceptual profile normal to the Banda detachment, from inside the Banda inner arc to just outside the Banda outer arc, illustrating the relationship between the Banda detachment and Tanimbar–Seram fold-and-thrust belt used to model the GPS velocities in a and the hyper-extended lithosphere underlying the Weber Deep. The black symbols denoting fault slip indicate the sense of long-term fault slip; note that these are opposite in sense to the ‘backslip’ applied to model the interseismic deformation.
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As the world’s largest archipelagic country in Earth’s most active tectonic region, Indonesia faces a substantial earthquake and tsunami threat. Understanding this threat is a challenge because of the complex tectonic environment, the paucity of observed data and the limited historical record. Here we combine information from recent studies of the...
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... long been debated: Anderson-Byerlee fault theory predicts that LANFs should frictionally lock up and be abandoned in favor of new steeply dipping normal faults [12][13][14] . Nonetheless, recent paleoseismic evidence [15][16][17][18] has shown that LANF systems host large earthquakes that rupture multiple segments of interconnected fault networks. Furthermore, although earthquakes of up to M w 6.8 have been reported on LANFs worldwide 13,14,[19][20][21][22][23] , multifault LANF ruptures may explain why M w > 7.0 earthquakes with well-resolved LANF nodal planes are absent in the modern instrumental record: seismic waveforms used in moment tensor inversions sample energy from all rupturing fault segments, and the contribution from LANF slip may be overprinted by simultaneous seismic slip on more steeply dipping faults 18 . ...
Despite a lack of modern large earthquakes on shallowly dipping normal faults, Holocene Mw > 7 low-angle normal fault (LANF; dip<30°) ruptures are preserved paleoseismically and inferred from historical earthquake and tsunami accounts. Even in well-recorded megathrust earthquakes, the effects of non-linear off-fault plasticity and dynamically reactivated splay faults on shallow deformation and surface displacements, and thus hazard, remain elusive. We develop data-constrained 3D dynamic rupture models of the active Mai’iu LANF that highlight how multiple dynamic shallow deformation mechanisms compete during large LANF earthquakes. We show that shallowly-dipping synthetic splays host more coseismic slip and limit shallow LANF rupture more than steeper antithetic splays. Inelastic hanging-wall yielding localizes into subplanar shear bands indicative of newly initiated splay faults, most prominently above LANFs with thick sedimentary basins. Dynamic splay faulting and sediment failure limit shallow LANF rupture, modulating coseismic subsidence patterns, near-shore slip velocities, and the seismic and tsunami hazards posed by LANF earthquakes.
... We synthesize the previous regional GPS studies in conjunction with newly available geologic and seismologic observations from across the region to develop a consistent and coherent kinematic description for the whole IANGCZ. Cloos (2005), Cummins et al. (2020), François et al. (2016), Jaya and Nishikawa (2013), Koulali et al. (2015), and Spencer et al. (2016). Faults are from the East and Southeast Asia (CCOP) 1:2,000,000 geological map (downloaded from https://www.orrbodies.com/resource/ccop-geology-south-east-asia/). ...
... In one of the most recent GPS studies of eastern Indonesia, Koulali et al. (2016) divided the Sunda-Banda Arc into the three microblocks: East Java, Sumba, and Timor (EJAV, SUMB, and TIMO, respectively, in Figure 3). Taking six new GPS velocities located in the Banda area into account, Cummins et al. (2020) revised the block geometry Figure S4a and Figure S4b of Supporting Information S1, respectively. of Koulali et al. (2016) by using the active Banda detachment fault as a block boundary that separates the Banda block of Koulali et al. (2016) into the two microblocks, Banda and Seram (BAND and SERA in Figure 3a). ...
... All the GPS velocities and earthquake slip vectors are inverted simultaneously to estimate the Euler vectors of blocks and coupling fractions, defined as the ratio of locked to total slip on the major block boundary faults. Block boundaries are the most important prerequisites for the inversion, and they were initially determined from the seismicity (Mw ≥ 5) distribution (Figure 2), GPS velocity field (Figure 2), mapped faults (Figure 1), and the models from previous studies (e.g., Bock et al., 2003;Cummins et al., 2020;Koulali et al., 2015Koulali et al., , 2016Stevens et al., 2002;Wallace et al., 2004Wallace et al., , 2014. The choice of threshold magnitude for earthquake data varies among the previous kinematic studies, which choose a similar or even smaller magnitude threshold than used here for the initial boundary determination (Koulali et al., 2015(Koulali et al., , 2016Reilinger et al., 2006;Wallace et al., 2004Wallace et al., , 2014. ...
The Indonesia‐Australia‐New Guinea collision zone comprises a complex system of tectonic blocks whose relative motion accommodates convergence of the Sunda Block, Pacific, Australian, and Philippine Sea plates. Previous studies have considered either the western or eastern ends of this system, in eastern Indonesia and Papua New Guinea, respectively. However, these studies had limited ability to characterize either the kinematics of the central part of the system or transitions in tectonic regime across it. In this study, we perform a simultaneous inversion of 492 earthquake slip vectors and 267 GPS velocities to quantify the block movement spanning the Sunda‐Banda Arc, Western New Guinea, and Papua New Guinea. Our best‐fitting kinematic block model comprises 23 elastic blocks, for which we estimate the rotation rates and block boundary slip rates. We show how the Cenderawasih Bay sphenochasm was likely formed by a combination of both rotations (2.82 ± 0.11°/Myr anticlockwise) of the Bird's Head Block and southwest‐directed convergence (39.9 ± 1.7 mm/yr) along the Lowlands fault. Our estimated relative slip vectors across the New Guinea Fold‐and‐Thrust Belt indicate a transition in the tectonic regime of the block boundary from predominately thrust faulting at its western segment, with a convergence rate up to 19.5 ± 0.6 mm/yr, to predominately sinistral motion in the center segment with slip rate ∼7 mm/yr, and returning to thrust in the eastern segment with a convergence rate up to 9.0 ± 0.5 mm/yr, implying the combined effect of multiple driving mechanisms.
... They contain a number of minerals, including zircons and micas, which can be precisely dated ( Pownall et al., 2014( Pownall et al., , 2017a( Pownall et al., , 2017b, and provide ages complementing the few previous K-Ar, 40 Ar/ 39 Ar, and Rb-Sr ages. They record multiple episodes of melting and metamorphism during extension caused by Miocene-Pleistocene subduction rollback, which continues today ( Pownall et al., 2016 ;Cummins et al., 2020 ). Like the Sulawesi metamorphic and igneous rocks ( Hennig et al., 2017 ) they record very young and extremely rapid exhumation. ...
In the Neyriz area of southern Iran unusual skarns are found above serpentinised peridotites at the contact with crystalline limestones. They have been interpreted as the high-temperature product of intrusion by hot peridotite into limestones, as low-temperature rodingites (the product of calcium metasomatism associated with serpentinisation), or a fortuitous juxtaposition of unrelated rocks. Their age is not known. The skarns are wollastonite-pyroxene-calcite rocks in which dark green pyroxenes are fassaites
with high Al, Fe and Ti with high Ca-Tschermak’s components. The field relations, textures, mineral assemblages and compositions, and melt inclusions in wollastonite and fassaite indicate the skarns formed by melting at the contact between peridotites and limestones with retrograde reactions during cooling forming garnet and anorthite. There are uncertainties in temperature estimates since pressure, X CO2 and other compositional variables are unknown, but melting temperatures were likely to have been close to 1100° C with garnet formation at approximately 900° C. Later alteration of some skarns and formation
of rodingites close to the limestone-peridotite contacts occurred during low-temperature Ca metasomatism, probably after emplacement of the ophiolite during Zagros collision. A hot intrusive origin for the skarns appears incompatible with an arc-related supra-subduction origin of the ophiolite inferred from geochemical studies, but recent work in eastern Indonesia shows that during late Neogene subduction
rollback, melts formed above hot mantle that intruded highly extended continental crust in a forearc setting. The scale, timing and temperatures of melting and metamorphism are very similar to those of the Late Cretaceous Neyriz ophiolite.
... This was among the reasons Fisher and Harris (2016) concluded that a great (M w 8.5) earthquake had occurred in the Banda Sea. But other studies (Marliyani et al., 2019;Cummins et al., 2020) have inferred that the accounts from east Java and the Banda Sea area refer to separate, smaller events. Adding to the uncertainty, Anonymous (1852) says that the shocks in east Java were felt on 26 November (repeated by Wichmann, 1918), but later Anonymous (1853) citing the Javasche Courant (18 December 1852, v101) says 23 November 1852. ...
... With this in mind, we considered our macroseismic intensities alongside published MMI datasets for four well-documented nineteenth-century earthquakes (Fisher and Harris, 2016;Griffin et al., 2019;Cummins et al., 2020). Macroseismic intensities from these previous published studies were not converted from one scale to another as a rule (Ambraseys et al., 1983) unless we could re-evaluate them from an original source. ...
... We then calculated the absolute median difference (MDIF) of Δ Intensity for each dataset being compared to Gempa Nusantara. Our comparisons display good agreement between the macroseismic intensities in our database and those from Griffin et al. (2019; Fig. 8a,b) and Cummins et al. (2020;Fig. 8c) for which MDIF values for Δ Intensity were, on average, one unit of intensity. ...
We present a new database called Gempa Nusantara, which is a collection of 7380 macroseismic observations for 1200 historical earthquakes in Indonesia between 1546 and 1950 C.E. using the European Macroseismic Scale (1998). Scrutinizing preserved original, first‐hand, private, and official documentation from the colonial period in Indonesia, we could examine the completeness of this written record based on the gradual expansion of European influence in the Indonesian Archipelago. As the largest database of uniformly assessed macroseismic intensities ever assembled for Indonesia, our database can correct errors and fill gaps in other contemporary studies of historical Indonesian earthquakes, as well as paleoseismic studies such as the coral paleogeodetic record from Sumatra. Remarkably, given the presence of several major active faults, conclusive evidence of coseismic surface ruptures during the colonial period was limited to just two events in 1909 and 1933. Our reliance on original materials also allowed us to document extreme coseismic ground failure in Sumatra in 1936 with striking similarities to those observed on Sulawesi in 2018. From the perspective of seismic hazard in a rapidly urbanizing nation, we show that the frequencies of observed intensities over the duration of our database correspond with modern seismic hazard curves from recent publications by other authors for 12 Indonesian cities, including Jakarta, with some notable exceptions such as Ambon and Yogyakarta. In summary, our work on Gempa Nusantara demonstrates how a carefully vetted and well‐documented historical record not only compliments studies of seismic hazard but is also itself an important standalone tool for the study of earthquake hazards in Indonesia.
... These tectonic features show complex behavior, and controversies have surrounded their origins and seismic behavior Patria and Hall, 2017). In terms of seismic activities, the region experienced devastating earthquakes and tsunamis, among which are the major events in 1629, 1674, 1852, and 1899(Wichmann, 1918Berninghausen, 1966;Latief et al., 2000;Brune et al., 2010;Liu and Harris, 2014;Fisher and Harris, 2016;Cummins et al., 2020;Pranantyo and Cummins, 2020). The source regions and detailed impacts of many historical events in this region are not known due to the lack of instrumental data and paucity of historical records. ...
... In the Banda Sea region, the Weber Deep is a prominent 7.2-km-deep basin derived from the extensional tectonics of the active Banda detachment fault (Pownall et al., 2016). Submarine landslides on the eastern wall of the Weber deep might be triggered by earthquakes and cause tsunamis ( Fig. 7a; Hall et al., 2017;Cummins et al. 2020). The offshore south Seram is characterized by steep bathymetric slopes, up to 23°, with a maximum depth of about 4 km (Fig. 7b). ...
A 51 cm tsunami amplitude was observed in Tehoru, Seram Island (Indonesia), following an Mw 5.9 earthquake. Such a relatively large tsunami is highly unexpected from this size earthquake. Our analyses showed that the tsunami was 15 times larger in Tehoru tide gauge station than that recorded on two other stations located nearby. These observations imply that the tsunami was most likely generated by a secondary source such as a submarine landslide that potentially occurred near Tehoru. Local people reported landslide activities around Tehoru following the earthquake. We conducted numerical modeling of the tsunami by considering the tectonic source and found that the resulting tsunami was only a few centimeters in Tehoru. Therefore, it is very likely that the earthquake was not responsible for the tsunami observed in Tehoru. By assuming that a submarine landslide was responsible for the tsunami, we applied spectral analysis and tsunami backward raytracing to gain information about the potential size and location of the landslide. Backward raytracing was also applied to identify the earthquake source of the tsunami. Numerical modeling of eight candidate landslide scenarios showed that a landslide with a length and a thickness of approximately 4 km and 50 m, respectively, was potentially responsible for the tsunami. We note that our results serve only as the first and preliminary estimates. Bathymetric surveys and high-resolution bathymetry data are essential to provide more detailed information about the landslide.
... Regardless of their tectonic and mechanical origins, active LANFs may pose significant seismic hazards to nearby communities due to the possibility of strong ground motion, landslides, and/or tsunamis associated with large LANF earthquakes (e.g., Cummins et al., 2020). Further constraints on the physics of LANF earthquakes and the mechanical conditions promoting shallow coseismic slip are needed to improve estimates of the seismic hazard potential of these faults. ...
... The local coral paleoseismologic record suggests it hosts infrequent M w 7.0+ earthquakes. Recent targeted studies provide a wealth of geologic and geophysical observations illuminating the strength, stress, structure and deformation of the Mai'iu fault (Figures 1 and 2), providing the necessary ingredients (Section 2) for realistic data-constrained dynamic rupture models that are missing from other proposed seismogenic LANFs like the submarine Moresby Seamount fault (Abers, 2001) and Banda detachment (Cummins et al., 2020) or the buried LANF segment inferred to have slipped during the 2010 El Mayor-Cucapah earthquake (Fletcher et al., 2016). In addition, low-angle slip in modern LANF earthquake candidates remains contested: for example, geodetic (Gonzalez-Ortega et al., 2014) and dynamic rupture (Kyriakopoulos et al., 2017) models explain many features of the 2010 El-Mayor Cucapah event with slip on only steeply dipping normal faults and no slip on the underlying LANF inferred by Fletcher et al. (2016). ...
... Our models suggest that LANFs are dynamically viable under common crustal loading conditions, yet they do not fully resolve the perplexing scarcity of large earthquakes with well-resolved low-angle normal-sense focal mechanisms in the modern instrumental record (Collettini & Sibson, 2001;Jackson & White, 1989), for which various mechanical explanations have been proposed. Wernicke (1995) posited that LANF earthquakes are particularly rare because these faults typically accommodate relatively slow extension rates (a few mm/yr) and thus host only infrequent earthquakes; however, faster extension rates ≥1 cm/yr across the Mai'iu fault Wallace et al., 2014;Webber et al., 2018) and the Banda detachment (Cummins et al., 2020) suggest these LANFs should host more frequent earthquakes. Nonetheless, paleoseismically recorded recurrence intervals from the Goodenough portion of the Mai'iu fault range from 482 to 1,590 years (Biemiller, Taylor, et al., 2020). ...
Despite decades‐long debate over the mechanics of low‐angle normal faults (LANFs) dipping less than 30°, many questions about their strength, stress, and slip remain unresolved. Recent geologic and geophysical observations have confirmed that gently dipping detachment faults can slip at such shallow dips and host moderate‐to‐large earthquakes. Here, we analyze the first 3D dynamic rupture models to assess how different stress and strength conditions affect rupture characteristics of LANF earthquakes. We model observationally constrained spontaneous rupture under different loading conditions on the active Mai'iu fault in Papua New Guinea, which dips 16°–24° at the surface and accommodates ∼8 mm/yr of horizontal extension. We analyze four distinct fault‐local stress scenarios: (1) Andersonian extension, as inferred in the hanging wall; (2) back‐rotated principal stresses inferred paleopiezometrically from the exhumed footwall; (3) favorably rotated principal stresses well‐aligned for low‐angle normal‐sense slip; and (4) Andersonian extension derived from depth‐variable static fault friction decreasing toward the surface. Our modeling suggests that subcritically stressed detachment faults can host moderate earthquakes within purely Andersonian stress fields. Near‐surface rupture is impeded by free‐surface stress interactions and dynamic effects of the gently dipping geometry and frictionally stable gouges of the shallowest portion of the fault. Although favorably inclined principal stresses have been proposed for some detachments, these conditions are not necessary for seismic slip on these faults. Our results demonstrate how integrated geophysical and geologic observations can constrain dynamic rupture model parameters to develop realistic rupture scenarios of active faults that may pose significant seismic and tsunami hazards to nearby communities.
... For instance, buildings in West Java Province are also susceptible to strong wind incidents [68]. Other disasters such as land subsidence [69,70], volcanic eruption [71,72], tsunami [73,74], and wildfire [75,76] should be considered in Indonesia. This multi-hazard analysis and comfort index could be applied in other potential sectors such as transportation [77] or other infrastructure developments such as power plants [78] and river networks [79]. ...
This study proposes a new model for land suitability for educational facilities based on spatial product development to determine the optimal locations for achieving education targets in West Java, Indonesia. Single-aspect approaches, such as accessibility and spatial hazard analyses, have not been widely applied in suitability assessments on the location of educational facilities. Model development was performed based on analyses of the economic value of the land and on the integration of various parameters across three main aspects: accessibility, comfort, and a multi-natural/biohazard (disaster) risk index. Based on the maps of disaster hazards, higher flood-prone areas are found to be in gentle slopes and located in large cities. Higher risks of landslides are spread throughout the study area, while higher levels of earthquake risk are predominantly in the south, close to the active faults and megathrusts present. Presently, many schools are located in very high vulnerability zones (2057 elementary, 572 junior high, 157 senior high, and 313 vocational high schools). The comfort-level map revealed 13,459 schools located in areas with very low and low comfort levels, whereas only 2377 schools are in locations of high or very high comfort levels. Based on the school accessibility map, higher levels are located in the larger cities of West Java, whereas schools with lower accessibility are documented far from these urban areas. In particular, senior high school accessibility is predominant in areas of lower accessibility levels, as there are comparatively fewer facilities available in West Java. Overall, higher levels of suitability are spread throughout West Java. These distribution results revealed an expansion of the availability of schools by area: senior high schools, 303,973.1 ha; vocational high schools, 94,170.51 ha; and junior high schools, 12,981.78 ha. Changes in elementary schools (3936.69 ha) were insignificant, as the current number of elementary schools is relatively much higher. This study represents the first to attempt to integrate these four parameters—accessibility, multi natural hazard, biohazard, comfort index, and land value—to determine potential areas for new schools to achieve educational equity targets
... However, in the Maluku sea plate we found normal events at shallow depth. The shallow normal events might be related to complex collision; and might pose a tsunami hazard [13]. We plotted the normal mechanisms in a map view and cross-section in figure 4. We further assessed the stress direction in the Maluku sea plate region. ...
Present day Molucca or Maluku sea plate in the eastern of Indonesia possesses a complex tectonic setting. This complex tectonic setting has been formed due to the collision of an actively moving Eurasian plate and Philippine sea plate toward the Maluku sea plate. At the west, Maluku sea plate is subducting beneath Sangihe arc, which began in the early Miocene. While at the east, Maluku sea plate is subducting under Halmahera arc, since in the middle Miocene. These subduction processes take place up to the present. Therefore, it has formed Maluku sea plate into an inverted U-shape slab under a thickening accretionary complex. Seismicity distribution has clearly shown the U-shape slab. Earthquake events take place on the subducting slab, and interestingly on the above accretionary complex as well. Maluku sea plate might pose hazards to surrounding islands: northern Sulawesi, Halmahera island, Sangihe island and Talaud island. The possible hazard, for instance, a thrusting earthquake which may generate tsunami to the nearby islands. Hence, understanding its tectonic and seismicity signature, especially at the shallow part, are indeed important in the Maluku sea region. Faulting regime could be analyzed using focal mechanism ternary diagram analysis, by categorizing the focal mechanisms’ strike, dip and rake values. Thus, in this study we aim to analyze faulting regime and hazard potential in the complex. Maluku setting using ternary diagram analysis.
... Historical accounts in Indonesia were mostly available on a description data-types and incomplete (e.g. [7,8,9] Figure 1. a) Tectonic setting of Sulawesi Island. ...
We studied the February 23rd, 1969 M7.0 Majene, Sulawesi earthquake and tsunami. It was followed by tsunami reported at five locations. At least 64 people were killed and severe damage on infrastructures were reported in Majene region. Based on damage data, we estimated that the maximum intensity of the earthquake was MMI VIII. Focal mechanisms, derived using first motion polarity analysis, indicated that the earthquake had a thrust mechanism. Furthermore, we built hypothetical earthquake scenarios based on a rectangular fault plane of 40 km × 20 km with a homogeneous slip model of 1.5 m. We run the Open Quake and the JAGURS code to validate the macroseismic and tsunami observation data, respectively. Our best-fitted earthquake model generates maximum intensity of 8+ which is in line with the reported macroseismic data. However, the maximum simulated tsunami height from all scenario earthquakes is 2.25 m which is smaller than the 4 m tsunami height observed at Pelattoang. The possibility of contribution of another mechanism to tsunami generation requires further investigation.
... Previous efforts to reconstruct pre-instrumental earthquakes have varied from a focus on the use of geological evidence (see [34,49,23,32] for example) to the use of historically recorded (but not instrumental) accounts [40,4,29,21,44,11,18,6,42] as well as some combination of the two types of uncertain data (see [31] for one example). Most of these efforts, particularly those directed toward using historical records, have relied on a combination of physical intuition and a restricted number of forward simulations to match the observational data. ...
... Here f is an observable, which we will consider to be our six earthquake parameters, V denotes variance, and the sensitivity bound S f,v is the approximate derivative of E P θ [f ] with respect to perturbation of θ in the direction of v. (6) shows that the greatest sensitivity will occur when the perturbation v heavily weights likelihood parameters θ that most affect the posterior (the second term) and earthquake parameters f have the most uncertainty in the posterior (the first term). To estimate the worst-case scenario, we again assume here that the perturbation v is along the first singular vector of I. ...
We apply the Bayesian inversion process to make principled estimates of the magnitude and location of a pre-instrumental earthquake in Eastern Indonesia in the mid 19th century, by combining anecdotal historical accounts of the resultant tsunami with our modern understanding of the geology of the region. Quantifying the seismic record prior to modern instrumentation is critical to a more thorough understanding of the current risks in Eastern Indonesia. In particular, the occurrence of such a major earthquake in the 1850s provides evidence that this region is susceptible to future seismic hazards on the same order of magnitude. More importantly, the approach taken here gives evidence that even "small data" that is limited in scope and extremely uncertain can still be used to yield information on past seismic events, which is key to an increased understanding of the current seismic state. Moreover, sensitivity bounds indicate that the results obtained here are robust despite the inherent uncertainty in the observations.
