Future Large Earthquake Analysis of Sulawesi Island Using Satellite Images and Moment Tensor Solution Approach

Sulawesi Island is the active tectonic region, where the tectonic architecture and potential earthquake sources until now remain largely unknown. The worst earthquake, an Mw 7.5 on September 28, 2018, in Palu, Indonesia, was caused catastrophic damage to life and property. The earthquake has highlighted the urgent need to raise knowledge of the cause of possible large future earthquakes and vulnerability. The main objective for this project is to create a thorough earthquake probabilistic hazard analysis map of the region, which is presently unavailable to better prepare for future earthquakes. The neotectonic and structural map was created using was supplemented with the 30-m resolution Shuttle Radar Topography Mission, Centroid Moment Tensor (CMT) solution, and seismologic data. The results demonstrate that faulting controls the geometry and the majority of these faults are active and capable of causing medium to large magnitude earthquakes with moment magnitudes ranging from 6.2 to 7.5 from 44 seismic sources. Our results show Sulawesi's northern deformation regimes have high seismicity risk and vulnerability. This study contributes a realistic seismic source for the Sulawesi neotectonic area particularly at the northwest, north, and east deformation regime, to understand the key large future earthquakes.

Coastal vulnerability mapping due to tsunami using Geographic Information System in Buleleng Regency, Bali Province

Bali is one of the areas vulnerable to disasters because of its geographical position, which is flanked by two earthquake sources in the form of a subduction zone and back-arc thrust zone, which can cause a tsunami in Bali region. This research aims to identify and map the level of coastal vulnerability to the tsunami in Buleleng Regency, Bali Province. The mapping was carried out using Geographic Information System (GIS). This study used secondary data and field data. The parameters used in analyzing the level of tsunami vulnerability were land elevation, slope, landuse, distance from the beach, and distance from the river. The level of vulnerability was grouped into five classes, namely very safe (35,466.9 ha), safe (70,485.0 ha), moderately vulnerable (17,645.0 ha), vulnerable (6,903.3 ha), and very vulnerable (438.9 ha) located in the Districts of Gerokgak, Seririt, Buleleng, and Sawan which are close to the river.

Fault Activation in Central Mongolia during the Holocene: Results of Study of the Mogod Earthquake Ruptures

—In order to determine the seismotectonic activity of faults in the Holocene, we performed trench studies of the ruptures produced by the catastrophic Mogod earthquake (5 January 1967, M = 7.5–7.8, I0 = 9–10) in the junction zone of the N–S striking Hulzhin Gol fault and the NW striking Tullet fault. Paleoseismic interpretation of seismic-deformation sections and radiocarbon dating of the samples allowed determining the kinematics and obtaining, for the first time, the absolute ages of paleoevents preceding the Mogod earthquake. Analysis of the tectonic conditions for realization of earthquake sources has shed light on the complex structure of ruptures in the area of the Mogod earthquake epicenter, within which three segments differing in the displacement amplitudes and kinematics have been identified. The research data indicate the repeated activation of the Tulet and Hulzhin Gol faults in the Late Pleistocene–Holocene. The absolute age of the latest activation is 596–994 AD for the Tulet fault and 11,379–6235 BC for the Hulzhin Gol fault. The cumulative deformation from paleoearthquakes in the trench sections in the Tulet fault zone points to at least two displacements of thrust kinematics, with the latest of them having an amplitude of 2.8 m. The paleoearthquake in the Hulzhin Gol fault zone is characterized by the presence of lateral slip. The amplitudes of deformations attest to earlier earthquakes similar in energy to the 1967 Mogod event or even stronger in the fault node. The obtained data on the timing of these earthquakes and the amplitudes of the accompanying displacements made it possible to estimate slip rates along the faults: 0.2–0.3 m/kyr horizontal-slip rates on the Hulzhin Gol fault and 0.5–0.7 m/kyr vertical-slip rates on the Tulet fault.

Study on the characteristic mechanisms of infrasonic precursors during the damage process of impending earthquake sources

Infrasonic signals measured before an earthquake carry information about the size and development speed of the source fracture, the stress at the fracture site and the elastic properties of the geologic medium. The infrasonic signal has a stable time scale, and compared with other precursors, infrasound has a unique sensitivity to earthquake disasters. However, to date, there has been no relevant theoretical research on the mechanism of infrasonic anomalies, and information on the development of fracture sources cannot be obtained from these characteristics, which makes the application of this anomaly in earthquake prediction challenging. In this study, we obtained the characteristics of short-term and impending infrasonic anomalies based on the infrasound data of more than 100 strong earthquakes. With a range of elastic medium models with a large number of fractures, we completed the theoretical simulation of the formation process of infrasonic precursors during the formation of the main fractures, analyzed the physical evolution of acoustic signals when cracks are generated, and quantitatively described the stages of large fracture formation caused by the initiation and propagation of seismic cracks. Specifically, this study revealed the causes of various and complex forms of infrasonic precursors near the critical point and the causes of the time- and space-dependent characteristics of these precursors, such as a noticeable attenuation of the pulse number, a low frequency and a large amplitude, which verified the effectiveness of infrasonic anomalies as strong earthquake precursors.

Early assessment of seismic hazard in terms of Voronezh massif-Moscow Depression contact

Purpose is to develop a system approach for early assessment of areas being of high seismic hazard and characterizing by low stability of rock mass relative to external loads. Methods. Well cores have been assessed down to 30 depth and seismic observations have been accumulated. Complexes of field geophysics methods have been applied for the research as well as remote sensing materials, digital model of surface relief, and techniques of qualitative and quantitative interpretation. Findings. Seismic hazard map has been formed in terms of seismic intensification and ground displacement units. The abovementioned is quite reliable but a cost-based result involving early assessments of high seismic hazard areas to infill network of geophysical measurements in the neighbourhood of the areas for their further quantitative characterization. It has been identified that rare well network and definite geophysical lines, run under conditions of a complex terrain, cannot localize the areas of high seismic hazard to focus builders on the enforcement of certain components of the erected structures. It has been defined that end result of the prognostic developments takes a shape of mapping of local areas with the decreased stability of upper share of the geological section supported by further measurements by means of a common depth point method (CDP). Comparison of potential secondary earthquake sources with high permeability zones makes it possible to predict highly reliable areas of the increased seismic magnitude. Originality.For the first time, interpretation techniques have been adapted to describe parametrically nonpotential geofields (i.e. optical density of remote basis; and relative elevation), accepted during the steps of potential field processing, with the use of wave analogies. Practical implications.The methods have been developed helping optimize field geological and geophysical operations in terms of area and well number as well as measuring stakes under the conditions of the limited prior data amount.

Probabilistic Tsunami Hazard and Risk Analysis: A Review of Research Gaps

Tsunamis are unpredictable and infrequent but potentially large impact natural disasters. To prepare, mitigate and prevent losses from tsunamis, probabilistic hazard and risk analysis methods have been developed and have proved useful. However, large gaps and uncertainties still exist and many steps in the assessment methods lack information, theoretical foundation, or commonly accepted methods. Moreover, applied methods have very different levels of maturity, from already advanced probabilistic tsunami hazard analysis for earthquake sources, to less mature probabilistic risk analysis. In this review we give an overview of the current state of probabilistic tsunami hazard and risk analysis. Identifying research gaps, we offer suggestions for future research directions. An extensive literature list allows for branching into diverse aspects of this scientific approach.

Seismic event detection in urban Singapore using a nodal array and frequency domain array detector: earthquakes, blasts and thunderquakes

Summary Detection of seismic events at or below the noise level is enabled by the use of dense arrays of receivers and corresponding advances in data analysis methods. It is not only important to detect tectonic events, but also events from man-made, non-earthquake sources and events that originate from coupling between the solid Earth and the atmosphere. In urban environments with high ambient noise levels the effectiveness of event detection methods is unclear, particularly when deployment restrictions result in an irregular receiver array geometry. Here we deploy a dense nodal array for 1 month in the highly populated city state of Singapore. We develop a new detection method based on image processing that we call spectrogram stacking, which detects anomalous, coherent spectral energy across the array. It simultaneously detects multiple classes of signal with differing spectral content and aids event classification, so it is particularly useful for signal exploration when signal characteristics are unknown. Our approach detects more local events compared to the traditional STA/LTA and waveform similarity methods, while all methods detect similar numbers of teleseismic and regional earthquakes. Local events are principally man-made non-earthquake sources, with several events from the same location exhibiting repeating waveforms. The closest earthquake occurs in peninsular Malaysia, in an area where no earthquakes have previously been detected. We also detect ground motion over a wide frequency range from discrete thunder events which show complex coupling between acoustic and elastic wavefield propagation. We suggest that care should be taken deciphering local high-frequency tectonic events in areas prone to thunder storms.

On possible relation of earthquakes with the sign change of the interplanetary magnetic field radial component

This work is devoted to an experimental study of the possible relationship between earthquakes and interplanetary magnetic field (IMF) variations. For the analysis, we use world and regional catalogs of earthquakes and a catalog containing data on the IMF sector structure for several decades. The main methodological technique consists in a comparative analysis of the occurrence rate of earthquakes on the days when Earth crosses the boundary between IMF sectors with the days when Earth is inside the sector. The sign of the IMF radial component is utilized as an indicator of the events on which the oscillation mode of Earth's magnetosphere depends. The sign reversal signals the probable crossing of the boundary between the IMF sectors by Earth, or, in other words, the crossing of the heliospheric current sheet by Earth. The hypothesis about the relationship between IMF variations and seismic activity is that IMF fluctuations, penetrating into the magnetosphere, excite ULF electromagnetic oscillations in the magnetosphere, which, in principle, can affect the physical processes in upcoming earthquake sources. We have found a weak, but statistically significant relationship between IMF variations and seismic activity. We also consider other IMF parameters that control ultra-low-frequency oscillations of the geomagnetic field.

On possible relation of earthquakes with the sign change of the interplanetary magnetic field radial component

This work is devoted to an experimental study of the possible relationship between earthquakes and interplanetary magnetic field (IMF) variations. For the analysis, we use world and regional catalogs of earthquakes and a catalog containing data on the IMF sector structure for several decades. The main methodological technique consists in a comparative analysis of the occurrence rate of earthquakes on the days when Earth crosses the boundary between IMF sectors with the days when Earth is inside the sector. The sign of the IMF radial component is utilized as an indicator of the events on which the oscillation mode of Earth's magnetosphere depends. The sign reversal signals the probable crossing of the boundary between the IMF sectors by Earth, or, in other words, the crossing of the heliospheric current sheet by Earth. The hypothesis about the relationship between IMF variations and seismic activity is that IMF fluctuations, penetrating into the magnetosphere, excite ULF electromagnetic oscillations in the magnetosphere, which, in principle, can affect the physical processes in upcoming earthquake sources. We have found a weak, but statistically significant relationship between IMF variations and seismic activity. We also consider other IMF parameters that control ultra-low-frequency oscillations of the geomagnetic field.