Summary On 28 September 2018, 18:02:44 local time, the Magnitude 7.5 earthquake accompanied by a tsunami and massive liquefaction devastated Palu region in Central Sulawesi, Indonesia. Comprehensive post-disaster surveys have been conducted, including field survey of surface ruptures, LiDAR, multibeam-bathymetry mapping, and seismic-reflection survey. We used these data to map fault ruptures and measure offsets accurately. In contrast to previous remote-sensing studies, suggesting that the earthquake broke an immature, hidden-unknown fault inland, our research shows that it occurred on the mappable, mature geological fault line offshore. The quake ruptured 177-km long multi-fault segments, bypassing two large releasing bends (first offshore and second inland). The rupture onset occurred at a large fault discontinuity underwater in a transition zone from regional extensional to compressional tectonic regimes. Then it propagated southward along the ∼110-km submarine fault line before reaching the west side of Palu City. Hence, its long submarine ruptures might trigger massive underwater landslides and significantly contribute to tsunami generation in Palu Bay. The rupture continued inland for another 67 km, showing predominantly left-lateral strike-slip up to 6-m, accompanied by a 5–10% dip-slip on average. The 7km sizeable releasing bend results in a pull-apart Palu basin. Numerous normal faults occur along the eastern margin. They cut the Quaternary sediments, and some of them ruptured during the 2018 event. Our fault-rupture map on mature straight geological fault lines allows the possible occurrence of early and persistent ‘supershear’, but significant asperities and barriers on segment boundaries may prohibit it.
Abstract. Twitter is an established social media platform valued by scholars as an open way to disseminate scientific information and to publicly discuss research results. Scientific discussions on Twitter are viewed by the media, who can then pass on information to the wider public. Social media is used widely by geoscientists, but there is little documentation currently available regarding the benefits or limitations of this for the scientist or the public. Here, we use the example of two 2018 earthquake-related events that were widely commented on by geoscientists on Twitter: the Palu Mw 7.5 earthquake and related tsunami in Indonesia and the long-duration Mayotte island seismovolcanic crisis in the Indian Ocean. We built our study on a content and contextual analysis of selected Twitter threads about the geophysical characteristics of these events. From the analysis of these two examples, we show that Twitter promotes a very rapid building of knowledge in the minutes to hours and days following an event via an efficient exchange of information and active discussion between the scientists themselves and the public. We discuss the advantages and potential pitfalls of this relatively novel way of making scientific information accessible to scholarly peers and lay people. We argue that scientific discussion on Twitter breaks down the traditional “ivory tower” of academia, contributes to the growing trend towards open science, and may help people to understand how science is developed and, in turn, to better understand the risks related to natural/environmental hazards.
Abstract. Twitter is an established social media platform valued by scholars as an open way to disseminate scientific information and to publicly discuss research results. Scientific discussions are widely viewed by the media who can then pass on information to the wider public. Here, we take the example of two 2018 earthquake-related events which were widely commented on Twitter by geoscientists: the Palu Mw 7.5 earthquake and tsunami in Indonesia and the long-duration Mayotte island seismo-volcanic crisis. We build our study on a content and contextual analysis of selected Twitter threads about the geophysical characteristics of these events. From the analysis of these two examples, we show that Twitter promotes very rapid building of knowledge – in the minutes to hours and days following an event – via an efficient exchange of information and active discussion between the scientists themselves and with the public. We discuss the advantages and potential pitfalls of this relatively novel way to make scientific information accessible to scholarly peers and to lay people. We argue that scientific discussion on Twitter breaks down the traditional ivory towers of academia, following growing trends towards open science, and may help people to understand how science is developed, and, in the case of natural/environmental hazards, to better understand their risks.
The Lembang Fault is a major fault located at the northern Bandung. This fault has a high disaster risk, including ground shaking, surface rupture, and possible landslides or liquefaction. This fault can cause earthquakes of 6.5-7 magnitude, making 8 million people in four Regencies and Cities around West Bandung Regency, Cimahi City, Bandung City and Bandung Regency exposed to major disaster risk. This research focuses on assessing the Perception of Disaster Proneness of the Lembang Fault in the District of Cisarua, West Java, Indonesia. This research was conducted using a case study and deductive-qualitative approach. In addition, this research was carried out by combining engineering and social research methodologies. The survey location point is determined based on hazard data (Peak Ground Acceleration data), vulnerability data (covering building density, slope, curvature, soil character, distance from faults, etc.) and population density data. This study indicates that the public’s perception of the disaster in the Lembang Fault is very subjective. How they act is based on experience or based on their beliefs. Therefore, an essential part of this research is assessing and measuring the community’s perception of the Lembang Fault towards disasters that may arise. The government must make serious efforts to convey that the disaster in the Lembang fault is much bigger and can happen at any time. Therefore, building resilient communities that genuinely understand the dangers of living in disaster-prone areas is essential.
The Java Back‐arc Thrust scars the entire back‐arc area of Java Island, but the faults' nature, timing, and activity remain partly elusive. Characterizing the structure and activity of the seismogenic Java Back‐arc Thrust (historical earthquakes up to 7 Mw) is a cornerstone to evaluate associated geohazards. We focus on the western part of Java Back‐arc Thrust that reaches the megalopolis of Jakarta. We combine morphotectonic data, seismic reflection, electric resistivity profiles, kinematic, structural field measurements, paleoseismological trenching, and sediment dating (optically stimulated luminescence and 14C). Our results suggest that the interplay between the faults, volcanoes, and sedimentary basin modulates the propagation of the fault system across and along‐strike. The West Java Back‐arc Thrust has been active from Pliocene to Recent, but with a laterally variable tempo and tectonic regime. While tectonic activity was sustained for longer times in the eastern part, the West Java Back‐arc Thrust broke through the Jakarta Basin in the west, possibly only since the Late Pleistocene, and partitions into a network of immature transpressive structures. We conclude that the West Java Back‐arc Thrust has a high seismic hazard that requires a careful risk evaluation along its trace, as it threatens the numerous infrastructures of the densely populated West Java.
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