#Evidence of #supershear during the 2018 magnitude 7.5 #Palu #earthquake from space geodesy (Nat Geosci., abstract)

[Source: Nature Geoscience, full page: (LINK). Abstract, edited.]

Evidence of supershear during the 2018 magnitude 7.5 Palu earthquake from space geodesy

Anne Socquet, James Hollingsworth, Erwan Pathier & Michel Bouchon

Nature Geoscience (2019)

 

Abstract

A magnitude 7.5 earthquake hit the city of Palu in Sulawesi, Indonesia on 28 September 2018 at 10:02:43 (coordinated universal time). It was followed a few minutes later by a 4–7-m-high tsunami. Palu is situated in a narrow pull-apart basin surrounded by high mountains of up to 2,000 m altitude. This morphology has been created by a releasing bend in the Palu-Koro fault, a rapidly moving left-lateral strike-slip fault. Here we present observations derived from optical and radar satellite imagery that constrain the ground surface displacements associated with the earthquake in great detail. Mapping of the main rupture and associated secondary structures shows that the slip initiated on a structurally complex and previously unknown fault to the north, extended southwards over 180 km and passed through two major releasing bends. The 30 km section of the rupture south of Palu city is extremely linear, and slightly offset from the mapped geological fault at the surface. This part of the rupture accommodates a large and smooth surface slip of 4–7 m, with no shallow slip deficit. Almost no aftershock seismicity was recorded from this section of the fault. As these characteristics are similar to those from known supershear segments, we conclude that the Palu earthquake probably ruptured this segment at supershear velocities.

Synthetic aperture radar data were processed using GMTSAR software, freely available from https://topex.ucsd.edu/gmtsar/.

Optical satellite images were mosaicked using the Geospatial Data Abstraction Library (http://gdal.org) and then correlated using the COSI-Corr software package available at www.tectonics.caltech.edu/slip_history/spot_coseis/download_software.html.

Deformation generated by a static earthquake source was modelled using Okada57 equations implemented in the disloc program (www.physics.hmc.edu/GL/disloc/disloc.c).

 

Data availability

The data sets generated during the current study (displacement fields from Landsat-8, Sentinel-2 and WorldView image correlation and from the ALOS-2 interferogram, as well as the static slip distribution) are available from the corresponding author upon request. Raw satellite optical imagery was made freely available by ESA (Sentinel-2, https://scihub.copernicus.eu/dhus/#/home), USGS (Landsat-8, https://earthexplorer.usgs.gov/) and DigitalGlobe (WorldView, www.digitalglobe.com/opendata/indonesia-earthquake-tsunami/). Raw ALOS-2 data availability is restricted to PI investigation at www.eorc.jaxa.jp/ALOS/en/aw3d30/data/index.htm.

 

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Keywords: Earthquakes; Tsunami; Geology; Indonesia.

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Giuseppe Michieli

I am an Italian blogger, active since 2005 with main focus on emerging infectious diseases such as avian influenza, SARS, antibiotics resistance, and many other global Health issues. Other fields of interest are: climate change, global warming, geological and biological sciences. My activity consists mainly in collection and analysis of news, public services updates, confronting sources and making decision about what are the 'signals' of an impending crisis (an outbreak, for example). When a signal is detected, I follow traces during the entire course of an event. I started in 2005 my blog ''A TIME'S MEMORY'', now with more than 40,000 posts and 3 millions of web interactions. Subsequently I added an Italian Language blog, then discontinued because of very low traffic and interest. I contributed for seven years to a public forum (FluTrackers.com) in the midst of the Ebola epidemic in West Africa in 2014, I left the site to continue alone my data tracking job.