Seismic activity and gravity field interpretation for subsurface fault detection on Mount Pandan, Indonesia

Problems Statement and Purpose. Northern Tanzania Volcanic terrain has been a subject of evaluation for geothermal potential in the last four decades. The region is characterized by Neogene to Recent volcanic and tectonic activities. This preliminary study based on remote sensing, water chemistry, gravity data, geological structures and volcanic centers distribution reports the geothermal manifestations identified and discusses the implications on geothermal fluid pathways. Oxygen-hydrogen isotope data from water samples indicate that there were involved in the hydrothermal system. Tectono-Volcanic Structures. The Northern Tanzania Divergence (NTD) area characterized by Neogene to Recent volcanic and tectonic activities. Recent volcanic and tectonic activities are ash cone and lava dome eruption at the floor of Meru crater a century ago, dyke intrusion and volcanic eruption south of Gelai volcano, and Oldoinyo-Lengai volcano, respectively. Fumarolic activities and hot springs are dominant in a relatively young volcanic area to the north-eastern and northern part of the NTD. Data and Methods. Shuttle Radar Topography Mission (SRTM), Landsat 8 Operational Land Imager (OLI) image, water isotope analysis and gravity data were used to extract and analyze the surface and subsurface geological lineaments and map the hydrothermal alteration zones in the study area. The hydrothermal alteration is used to evaluate and identify the permeable structures. Analysis and interpretation of the length and trends of extracted lineaments were used to investigate the tectonic evolution. Geological map of a study area was digitized from the existing geological maps and the age of rocks to delineate volcanic activity and associated lineaments based on the age of the lithological domain. Digital image processing was applied to enhance the visual interpretation. Gravity data were used to give insight into the subsurface structure in the study area. Results and Discussion. The higher δ 18O values and large deviation from meteoric water lines suggest that is due to the interaction of fluids with host rocks at elevated temperatures. These are consistent with open structures that act as conduits for fluid flow. The potential field gravity data reveal a basin-like structure trending in the NNW direction. The gravity data show that the basement units gradually deepen towards the central part and that it is controlled by two main fault systems that trend N-S and NW-SE respectively. The gravity data presented here provides new constraints on the tectonic evolution and geothermal resources of the study area.

In the present study, we have identified the tectonically active zones along the Island Belt Uplift (IBU), an upthrown block of E-W trending Island Belt Fault (IBF). Major and minor transverse faults have segmented the IBU into four sub-uplifts, viz. Pachham Uplift (PU), Khadir Uplift (KU), Bela Uplift (BU), and Chorar Uplift (CU) from west to east, respectively. The work includes geodetic and morphotectonic analysis of the IBU region. The Normalized Steepness Index (Ksn) analysis was performed supported by swath profiling to mark the tectonic activity variations along and across the strike of the IBF in the IBU region. Further, the Ksn contour map was prepared by using a power-law function of slope (S) of the longitudinal profiles of the river, concavity index (ө), and upstream area (A), which is an integral part of the Stream Power Incision Model (SPIM). The Ksn analysis suggests that the maximum amount of tectonic activity is restricted along the northern escarpment of the IBU, which falls in the vicinity of IBF and it's associated longitudinal and transverse faults. Based on the results of Ksn analysis, we have marked the tectonically active zones in the IBU region, which shows that amongst four sub-uplifts, the PU and BU were found most active (Zone-I), the KU expresses moderate activity (Zone-II), while CU demonstrated to be least active (Zone-III). The results were also confirmed by documentation of active tectono-geomorphic features like strath terraces, river offsets, straight fault scarps, triangular facets, linear valleys, fault ridges, Quaternary upwarps, laterally displaced crests and alluvial fans within the IBU. The active deformation pattern calculated using the Global Positioning System (GPS) data-set from 2009–2019 along IBU reveal maximum deformation rate of ∼2.5 ± 0.5 mm/yr in the PU, ∼2.0 ± 0.5 mm/yr in the BU while, the KU shows the deformation rate of ∼1.2 ± 0.5 mm/yr, which coincides well with the results of Ksn. The Ksn analysis results were also validated by comparing them with existing Gradient Length Anomaly (GLA) and Differential Interferometric Synthetic Aperture Radar (DInSAR) data. The ongoing tectonic activity in the study area is also manifested by the occurrence of moderate seismic activities in the identified active zones. The active tectono-geomorphic features and fault scarp geometry were analyzed and compared with the existing experimental models of basement fault and overlying sedimentary covers, which allow us to understand the nature of fault components of IBF. The analysis reveals that the IBF has been influenced by both dip-slip and strike-slip fault components of motion, which can be further confirmed by geophysical analysis. The results of Ksn analysis and field evidence were merged to prepare Active Fault Map of the IBU region that can be implemented for future seismic hazard assessment.

Java Island is part of the island arc influenced by subducting Indo-Australian beneath Eurasian tectonic plates, therefore there is high seismic activity and an active volcanic chain trending East-West. One of the volcanoes in Java Island is Mt. Pandan, northern part of Madiun, East Java region, which is known as one of the dormant volcano in the region. According to the list of volcanoes in Indonesia Mt. Pandan is not classified as an active volcano. The previous studies mentioned that Mt. Pandan is a modern volcano which is located in the Kendeng zone. On June 25, 2015, there was felt earthquake (M 4.2) causing several houses damaged around Mt. Pandan as reported by Agency for Meteorology, Climatology, Geophysics (BMKG), Indonesia and then in February 2016, more than twenty small earthquakes (M < 4) occurred again in the area. In order to understand the structure beneath Mt. Pandan, we have conducted gravity measurement and seismicity analysis through hypocenter relocation. Our results show prominent low gravity and density anomalies by forward modeling derived from residual anomaly around Mt. Pandan area. The clusters of small earthquakes appear at depths of less than 30 km beneath Mt. Pandan. The selected focal mechanism of the event in the area is left-lateral faulting in the north and oblique dominant thrust in the south of Mt. Pandan. Some indications related to submagmatic activities such as hot springs and warm ground is found. Our interpretation is this phenomenon may be related to tectonic and magmatic activities. On the other hand, it confirms also that Mt. Pandan is probably a modern volcanic center.

<p>Intra-continental abandoned rifts can fail for many reasons and are typically considered to be tectonically inactive. It is widely thought that the Oligo-Miocene Suez Rift, Egypt, which is located at the propagating northern end of the Red Sea spreading ridge, was abandoned in the Pliocene when motion between the African and Arabian plates was accommodated instead by the sinistral Dead Sea transform fault. However, local evidence for Plio-Quaternary normal faulting, the presence of uplifted Quaternary shorelines along the rift margins, and low-magnitude but widespread seismicity, together suggest the Suez Rift is tectonically active. Here, we present the first detailed analysis of this post-“abandonment” tectonic activity. We analyze the fluvial and tectonic geomorphology of the rift using freely available, 30 m-horizontal resolution digital elevation models (DEMs). These data reveal widespread normal fault offsets of Plio-Quaternary rocks at outcrop-to-basin scale, even in rift sectors >250 km north of the southern terminus of the rift. River morphology, tectonic knickpoints, normalized steepness indexes (ksn), and chi (χ) maps also provide evidence for relatively young faulting. Uplifted Quaternary shorelines show that active normal faults have footwall uplift rates of up to 0.125 mm/yr, even in locations >200 km north of the rift terminus, with these rates being relatively consistent for both rift margins. Our preliminary results provide clear evidence for young and ongoing tectonic activity in the Suez Rift and thus question the notion that this evolving plate boundary is currently in a state of complete tectonic quiescence. We speculate that the present tectonic activity in the Suez Rift results from the translation of far-field stresses imposed by the Afar plume, or by a recent change in the Eulerian pole of rotation between the African and the Arabian plates. Our results call for further analyses of the recent rifting in the Suez Rift and the exploration of recent activity in other “abandoned” rifts.</p>

Introduction:Coronae are ovoid tectonic and magmatic features that are unique to Venus. Because Venus is likely to be geologically active in the present day, yet lacks an apparent system of plate tectonics, understanding the relationship between coronae, volcanism, and tectonism is important to characterize Venus’s geology and geophysical state over its history. At long spherical harmonic wavelengths volcanoes and coronae often associated [1] but at regional scales there is a general anti-correlation related to spatial separation of volcanoes and coronae. A contextual view of this pattern is needed to understand the structures and processes underlying coronae formation and evolution.Taking advantage of recently produced global datasets for Venusian volcanoes [2] and coronae [3], we investigate the population density of volcanoes in and around coronae and for different geological units. The stand-out result is the lack of volcanoes in the region surrounding coronae relative to the population within coronae and other geological units, especially those of the plains which dominate the planet’s surface (Fig. 1). A possible interpretation of this pattern of volcanism is that the development of coronae erases preexisting geological features in their surroundings. Figure 1: Mean volcano densities, calculated for different geological units on Venus [4]. Rift zones exhibit the least volcanoes per unit area. It is likely that ongoing tectonic activity at rift zones erodes any volcanic edifice as fast or faster than they are formed. This contrasts with the plains units where any volcanism is likely preserved due to lesser impact of mechanical erosion or tectonic activity [5, 6]. Coronae and the circum-coronal regions (50% means the ring around the corona up to 1.5 times its radius from the center, 100% means the same but up to 2 times its radius) lie between these extremes, with more volcanoes in the corona than in its vicinity. Methods:If corona activity is erasing evidence of ongoing volcanism, then putatively active coronae (as defined by local gravity anomalies) should correlate with decreased volcano population densities in their vicinity compared to older, extinct coronae. To test this, we use Boolean statistical methods [7] to develop correlation indices between corona characteristics, geological context, and volcano populations (Fig. 2). Figure 2: Correlation indices between corona characteristics (rows) and volcano populations (columns), showing how the likelihood of a corona to have an area “clean” of volcanoes relative to its interior varies with corona morphology and geological context. Topographic Groups (TG) describe topographic profiles across coronae [8] and volcano population density is recorded in units of volcanoes per 100 km2. “Ring (100%)” refers to the thickness of the ring around the corona being 100% of the radius of the corona. Coronae in plains units are the most likely to exhibit a “clean” region in around them, while those in rifts and in deformed belts the least likely. If the morphology of a corona is domal or plateau-like (TGs 1, 2, 3,) or lacks a trough at its boundary than that corona is less likely to exhibit a clean cicrum-coronal region. These morphologies are strong correlated with being in a rift setting, suggesting a link between rifts, coronae, and patterns of volcanism.We also use terrestrial eruption rates to predict patterns of volcanism for different geological settings on Venus. By comparing predicted volcano populations to observed populations, as well as populations of volcanoes in and around coronae to the geological unit the corona is embedded in, the degree of volcanic activity can be characterized across Venus’ surface. If volcanic populations in the clean regions around coronae are reduced proportionally to the background rate of volcanism for that specific geological unit across all of Venus, than the suppression of volcanism is likely a result of coronae destroying evidence of volcanism in their vicinity. If not, then other factors, such as the thermal state and structure of the lithosphere, control the interactions between volcano populations and coronae. To further test this, we also look for evidence of deformed and embayed volcanoes in the vicinity of coronae in Magellan imagery. Results:We present the results of these analyses to constrain the degree of volcanic and tectonic activity for different geological settings, inside coronae, and in the coronal regions on Venus. Correlations between volcano populations, corona morphologies, and rift zones suggest that extensional, geodynamic processes may be interfering with the expression of volcanism around coronae. Outside of these zones, however, coronae generally lack evidence of volcanism in their vicinity, likely as a result of erosion or burial by tectonic and volcanic activity originating from the corona itself or by a geodynamic process that suppresses volcanism. Future work characterizing the geophysical properties of coronae (especially gravitational anomalies) and higher resolution maps will be able to definitely distinguish between these possibilities.

<p>The wider region around the city of Dubrovnik, encompassing coastal and offshore area of southern Croatia, is characterized by the relatively high seismicity rate with intermittent occurrence of strong events indicating the ongoing tectonic activity. Historical, instrumental and paleoseismological records show that this area was hit by at least dozen strong earthquakes in the last 500 years. Among these the most significant is the Great Dubrovnik earthquake from 1667 which devastated the region. This and other strong events of this area are related to several individual to composite seismogenic sources that generally extends in NW-SE direction from Albania to the central part of External Dinarides fold-thrust-belt in Croatia, still however, not yet sufficiently known in great details. Here, we aim to present preliminary results of identification and 3-D modeling of distribution and geometry of active faults in the offshore Dubrovnik area, based on analyses of reflection seismic profiles associated with deep borehole and surface geology data provided by the Croatian Hydrocarbon Agency.</p><p>Identification and classification of recently active faults in this area were performed by matching at least one of the following criteria: (1) offsets of the Pliocene - Quaternary deposits along faults that could be correlated between neighboring seismic lines, (2) deformation of Pliocene - Quaternary deposits above fault tips and (3) correlation of fault geometry and kinematics with distribution of the earthquake hypocenters and available fault plane solutions. In addition, a long-term neotectonic activity of identified faults has been studied by deformation and truncation of Miocene and Pliocene stratigraphic horizons that are frequently found affected by faults closely related with a long-term salt tectonics activity.</p><p>Location and geometry of the identified recently active faults are in good correlation with distribution of instrumentally recorded earthquake locations, where certain events are clustered within narrow zones of delineated fault planes. These preliminary results will be used for 3D geological and structural modelling of active earthquake generating fault systems between the city of Dubrovnik and the town of Ston, cross-section balancing and slip-rate calculation along active faults. In turn, these would provide input data for seismic shaking simulation and future seismic hazard assessment in this area.</p>

Insights into the “tectonic topography” of the present-day landscape of the central Iberian Peninsula (Spain)

In the Middle Atlas region, the Tizi N'Teghtène Fault System is a network of faults inherited from the Hercynian orogeny, which operated as normal faults during the Jurassic and reverse faults since the Miocene. The issue at hand is whether this fault system continues to be active today. To address this concern, focus has been placed on a central portion of the Tizi N'Teghtene Fault System, specifically the anticlinal ridge of Taïliloute. Determining the tectonically active segments of this ridge is crucial for structural analysis and the Quaternary evolution of this mountain chain. To achieve this, morphometric indices related to the evolution of watersheds and their streams have been employed. These indices include hypsometry, elongation ratio (Re), drainage asymmetry factor (AF), and the elongation profiles of various watercourses. These indicators provide insights into the degree of active longitudinal growth of the Taïliloute ridge. These parameters were determined through satellite image analysis using suitable software and geographic information systems (GIS). Tectonic activity analyses reveal that both flanks of this ridge exhibit ongoing tectonic activity, marked by the occurrence of normal faults and strike-slip faults during the Quaternary phase of the Alpine orogeny. It is concluded that the Tizi N'Teghtene Fault system remains tectonically active. This research contributes to a deeper understanding of the ongoing tectonic activities within the Tizi N'Teghtene Fault System, a matter of geological significance. By employing morphometric indices ad modern satellite image analysis techniques, a methodological innovation is presented by this study in assessing tectonic activity in mountainous regions. These results provide valuable insights into structural dynamics of the Middle Atlas, aiding in the understanding of its geological evolution. Furthermore, this research can have broader applications in seismic hazard assessment and land use planning, making it relevant beyond the immediate geographical boundaries of the study area.

Source and evolution of ore fluids in the Zhenyuan orogenic gold deposit, SE Tibet: Constraints from the S-C-O isotopes

Alteration and mineralization styles of the orogenic disseminated Zhenyuan gold deposit, southeastern Tibet: Contrast with carlin gold deposit

The Mugello Basin is a WNW-ESE-striking, seismically active intermontane basin currently experiencing post-orogenic extension that affects the hinterland of the Northern Apennines belt (Italy). It lies near the main watershed of the Northern Apennines, a feature traditionally seen as separating the internal, extension-dominated (to the southwest) part of the belt from the external, contractional (to the northeast) part. Therefore, complex and controversial relationships exist between the recorded seismic activity and the surface manifestations of potentially seismogenic faults at depth in the Mugello region. The ITaly HAzard from CApable faults (ITHACA) catalogue reports active and capable faults along both margins of the basin. Moreover, coseismic surface ruptures were observed during the 1919 earthquake. However, surface expressions of active faults in the Mugello region are less pronounced compared to those associated with similar graben-bounding faults in other intermontane basins of the Northern Apennines. Moreover, the subsurface structure of the basin remains poorly constrained and is widely debated, with a significant lack of reliable geophysical data. This has led to contrasting views on the size, geometry, and orientation of the potential seismogenic sources, according to different researchers. Thus, the Mugello Basin offers an excellent opportunity to apply geophysical surveys to address the gaps in knowledge regarding its subsurface structure.In this study, we used a combined methodological approach to propose a subsurface model for the basin's geometry and mechanical properties. We performed seismic microtremor measurements to be interpreted in the frame of the H/V and H&V methods along four profiles orthogonal to the basin’s axis (i.e., NNE-SSW) and one parallel to it (i.e., WNW-ESE). By integrating surface geological data and geomorphic analysis of the fluvial network (chi-map) based on a 10-m DEM, we were able to refine the geophysical model and more accurately evaluate the seismic behavior of the basin. We combined microtremor measurements with publicly available well log data and field geology observations, which helped us interpret the normalized H/V values and estimate the thickness of the basin’s sedimentary fill. Preliminary results suggest that the basin exhibits an asymmetric across-strike geometry, with active extensional faults likely concentrated along its northern margin. This is consistent with the epicentral distribution of seismic sequence that affected the area between 2009 and 2019, as highlighted by recent studies. Accordingly, geomorphic analysis shows the highest chi values in the northeast sector. This marks a disequilibrium of the river network which might be associated with active faulting, whereas in the southeast chi-values indicate steady state among rivers. The interpretation of the normalized H/V values in terms of bedrock geometry provides new insights into the basin's subsurface structure and offers constraints that challenge previously proposed models. These results have significant implications for evaluating seismic site effects at the scale of the Mugello Basin. Furthermore, they contribute to understanding the tectonic evolution of the basin within the larger geodynamic context of the Northern Apennines, particularly with respect to the transition from syn-orogenic compressive to post-orogenic extensional tectonics.

Tectonic geomorphology is a fast-developing interdisciplinary research field. Different from traditional geomorphology, tectonic geomorphology strongly shifts to quantify the geomorphic processes. The central tenet in tectonic geomorphology is to clarify the interactions among tectonic, climatic, and surface processes, and to provide quantitative descriptions of climate, topography, hydrology, physical and chemical erosion, deposition and rock deformation and their relationships in tectonically active settings. In this review, we first introduce major scientific questions and central concepts, the techniques and methods commonly used in this field, especially the major game-changing dating techniques (e.g., cosmogenic nuclide dating and low-temperature thermochronology) and remote sensing or surveying methods (e.g., LiDAR). Then we present some case studies in the past three decades showing lines of evidence that the interaction among tectonic, climatic, and surface processes can occur in a wide range of temporal and spatial scales, ranging from hours to million-year in time, and from single fault to orogenic belt in space. We also synthesize important progresses in this field toward a better understanding of the topographic evolution of orogenic belts: (1) Tectonic, climatic and surface processes collaborate to shape the landscape such that tectonic activities alone do not necessarily lead to topographic growth. For instance, when erosion and tectonic accretion are in equilibrium, topographic steady state is reached, with no surface uplifting despite on-going tectonic activity. (2) Sedimentary records in range-front basins, such as the increase of deposition rate, or the occurrence of conglomerates, were often used as proxies of tectonic uplift of mountain ranges in early studies. However, sedimentary sequence should be a collective product of tectonic, climatic, and surface processes. These commonly-used proxies for tectonic activity can also be due to climate changes, instead. (3) Tectonics plays a key and leading role in the coupling of tectonic-climatic-surface process; climatic and surface processes influence but do not drive tectonics. (4) Isostatic response to erosion will lead to the rebound of mountain peaks, but the overall effect of erosion is to lower the mean elevation. Thus, uplift due to isostatic rebound is a secondary component of tectonics. Lastly, we outline in brief a list of outstanding scientific questions remaining to be answered in the field.

Research in Lewa District, East Sumba Regency, Indonesia, aimed to identify mineral potential and clarify subsurface geological structures through gravity gradient analysis and 3D inversion modeling. This approach addresses the limitations of field gravity data in the study area. The gravity gradient method was chosen to delineate geological structure boundaries (such as formation contacts and faults) compared to conventional gravity methods and for processing global satellite data (GGMplus and EGM2008 derivatives of ERTM 2160) with limited measured data. Gravity gradient analysis, including vertical, horizontal gradient, and tilt angle, was applied to Complete Bouguer Anomaly data using 2D Fourier transformation. Gravity field correction in Lewa showed positive anomalies from volcanic basement rocks. The gradient analysis sharpened boundaries of anomalies linked to geological structures. Zero contours of vertical gradient and tilt angle defined structural boundaries, while peaks of horizontal gradient and tilt angle indicated metallic mineral sources. 3D gravity inversion modeling (density 2.22–2.97 g/cm³) showed rock intrusions at 215 meters depth, interpreted as key to mineralization formation. The 2D sections (A-A', B-B', C-C') contain Masu Formation volcanic rocks, with fault zones filled by Waikabubak Formation sedimentary rocks and silicified rocks from magma intrusion alteration. Fault systems were identified through vertical gradient extremes, representing contact formation. Highly positive contour values on the tilt angle map confirm the influence of the volcanic basement rock. Metal mineralization is closely related to tectonic activity and alteration from massive igneous intrusion. The integration of gravity gradient analysis and 3D inversion modeling has proven to be effective in mapping geological structures and identifying mineral prospects using limited data. These findings provide insights into the subsurface geology of Lewa and provide a basis for further mineral exploration in East Sumba.

The Albanian Dinarides represent the central segment of the Dinarides–Hellenides orogenic belt. The Albanian sector is strategically located at the boundary between continental subduction to the north and oceanic subduction to the south, making it an ideal setting to explore the interplay between surface and deep geological processes. Furthermore, modern seismicity (e.g. 1979, Mw 7.1 Montenegro, and 2019, Mw 6.4 Durres earthquakes) and geomorphic features indicate ongoing tectonic activity at least since the late Quaternary. In this study, we explore the landscape response to tectonics and climate by 1) conducting an extensive geomorphic analysis including knickpoint extraction, ksn and chi analysis, longitudinal river profile projection, and mapping of geomorphic features such as windgaps, river terraces, pediment surfaces and uplifted relict landscapes, and 2) estimating basin-wide denudation rates using cosmogenic nuclides.Specifically, we collected river sediment samples from more than 20 rivers draining all tectonic units and we determined denudation rates using the classic in situ 10Be technique for catchments draining quartz-bearing lithologies, and the new meteoric 10Be/9Be technique in carbonate and ophiolite settings where quartz-poor lithologies predominate. In a few cases, we used both techniques on the same catchments for inter-method comparison. The geomorphic analysis highlights the presence of river terraces, non-lithological knickpoints, uplifted relict landscapes and wind gaps suggesting recent tectonic activity at both regional and local scales. This led to a reshaping of the river network with changes in the hydraulic connectivity with the regional sea level that altered the sediment transport directions. Furthermore, Quaternary climatic variations appear to play a crucial role in the erosive power of rivers and in controlling cycles of aggradation and incision.Denudation rates show spatial variability, ranging from less than 0.3 mm/yr to 0.9 mm/yr in the south, where carbonate and siliciclastic predominate, to over 1 mm/yr in the central part of Albania, where siliciclastic rocks and ophiolites are widely exposed. Although the rates present a good correlation with geomorphic metrics (e.g., ksn and hillslope), the observed variability appears to be influenced by local tectonic processes associated with active normal faults and salt diapirism. Overall, the denudation rates obtained with the two Be techniques are consistent and align with published incision rates derived from river terrace dating, suggesting coupling between fluvial incision and hillslope processes over the last few thousands of years. The consistency between the two cosmogenic Be methods validates the high future potential of the meteoric 10Be technique in quantifying denudation rates in settings dominated by non-quartz lithologies.

Destructive earthquakes are frequently related to inland active faults. In recent years, a significant number of shallow earthquakes with low magnitude have occurred in southern Garut, West Java, Indonesia. Two earthquakes, with magnitudes of M4.2 and M3.9 in 2016 and 2017, respectively, have caused significant damage and were interpreted as indications of an active fault. We used publicly available gravity data to infer the subsurface structure that may be related to recent seismic activity. We used spectral analysis and filtering techniques for the regional-residual anomaly separation and anomaly enhancement to show the basin structure in the study area. 3D gravity inversion modelling was performed to obtain the subsurface density distribution. The result indicates the sedimentary layers with a density of 2.4 to 2.5 gr/cm3 with an underlying basement with a density of 2.65 gr/cm3. An intra-basin basement high with an NE-SW trend divides the basin into two sub-basins. This local basement high can be associated with a magmatic intrusion body and a series of young volcanic bodies located at the northeastern end of the basin. Our results emphasize a possible strong interaction between the tectonic and magmatic activities in this region.