On 28 September 2018, a strike‐slip earthquake occurred in Palu, Indonesia, and was followed by a series of tsunami waves that devastated the coast of Palu Bay. The tsunami was recorded at the Pantoloan tide gauge station with a peak amplitude of ~2 m above the water level and struck at high tide. We use the Pantoloan tsunami waveform and synthetic aperture rada displacement data in a joint inversion to estimate the vertical displacement around the narrow bay. Our inversion result suggests that the middle of the bay was uplifted up to 0.8 m, while the other parts of the bay subsided by up to 1 m. However, this seafloor displacement model alone cannot fully explain the observed tsunami inundation. The observed tsunami inundation heights and extents could be reproduced by a tsunami inundation simulation with a source model that combined the estimated vertical displacement with multiple subaerial‐submarine landslides.

We present the first continental‐scale seismic model of the lithosphere and underlying mantle beneath Southeast Asia obtained from adjoint waveform tomography (often referred to as full‐waveform 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 ∼13,000 unique source‐receiver pairs, we image isotropic P‐wave velocity, radially anisotropic S‐wave velocity and density via an iterative non‐linear inversion that begins from a 1‐D reference model. At each iteration, the full 3‐D 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 true‐amplitude data from events and receivers not included in the inversion. The trade‐off between inversion parameters is estimated through an analysis of the Hessian‐vector product. SASSY21 reveals detailed anomalies down to the mantle transition zone, including multiple subduction zones. The most prominent feature is the (Indo‐)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 S‐wave velocity zone beneath northern Borneo that may be associated with subduction termination in the mid‐late Miocene. A previously undiscovered feature beneath the east coast of Borneo is also revealed, which may be a signature of post‐subduction processes, delamination or underthrusting from the formation of Sulawesi.

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.

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Mt. Agung, located in Karangasem-Bali, Indonesia, had a significant increase of swarm earthquakes from September 2017 until the recent eruption in November 2017. To analyze the seismic swarm and its correlation with the magmatic movement, we worked on the regional seismic data recorded by Agency for Meteorology, Climatology and Geophysics of Indonesia (BMKG) between September 14 to October 20, 2017. P-and S-wave phases of the swarm events had been manually picked. In total, 804 events in the time period of September 14 to October 20, 2017 were successfully determined. To improve the location precision, the double-difference relocation method was performed. We identified most of the events as Volcano-Tectonic type A (VT-A) earthquakes and located between Mt. Batur and Mt. Agung. Those events form a cluster striking in NE-SW direction at a depth between 2 and 20 km. Focal mechanism solutions for selected events below Mt. Agung show a thrust and strike-slip faulting regime. Interestingly, a trend of event propagation toward the summit of Mt. Agung was observed. The frequency of VT-A event occurrences is significantly increased at the later stage of the swarms. We concluded that the increased seismic activity in Mt. Agung was due to the migration of magma from the deep chamber to the shallow reservoir.