The susceptibility of #Oklahoma’s #basement to #seismic #reactivation (Nat Geosci., abstract)

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

The susceptibility of Oklahoma’s basement to seismic reactivation

F. Kolawole, C. S. Johnston, C. B. Morgan, J. C. Chang, K. J. Marfurt, D. A. Lockner, Z. Reches & B. M. Carpenter

Nature Geoscience (2019)

 

Abstract

Recent widespread seismicity in Oklahoma is attributed to the reactivation of pre-existing, critically stressed and seismically unstable faults due to decades of wastewater injection. However, the structure and properties of the reactivated faults remain concealed by the sedimentary cover. Here, we explore the major ingredients needed to induce earthquakes in Oklahoma by characterizing basement faults in the field, in seismic surveys and via rock-mechanics experiments. Outcrop and satellite mapping reveal widespread fault and fracture systems with trends that display a marked similarity to the trends of recent earthquake lineaments. Our three-dimensional seismic analyses show steeply dipping basement-rooted faults that penetrate the overlying sedimentary sequences, representing pathways for wastewater migration. Experimental stability analysis indicates that Oklahoma’s basement rocks become seismically unstable at conditions relevant to the dominant hypocentral depths of the recent earthquakes. These analyses demonstrate that the geometry, structure and mechanical stability of Oklahoma’s basement make it critically susceptible to seismic reactivation.

Keywords: Geology; USA; Fracking; Earthquakes; Oklahoma.

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#Slip on a mapped normal #fault for the 28th December 1908 #Messina #earthquake (Mw 7.1) in #Italy (Sci Rep., abstract)

[Source: Scientific Reports, full page: (LINK). Abstract, edited.]

Article | OPEN | Published: 24 April 2019

Slip on a mapped normal fault for the 28thDecember 1908 Messina earthquake (Mw 7.1) in Italy

M. Meschis,  G. P. Roberts,  Z. K. Mildon,  J. Robertson,  A. M. Michetti &  J. P. Faure Walker

Scientific Reports, volume 9, Article number: 6481 (2019)

 

Abstract

The 28th December 1908 Messina earthquake (Mw 7.1), Italy, caused >80,000 deaths and transformed earthquake science by triggering the study of earthquake environmental effects worldwide, yet its source is still a matter of debate. To constrain the geometry and kinematics of the earthquake we use elastic half-space modelling on non-planar faults, constrained by the geology and geomorphology of the Messina Strait, to replicate levelling data from 1907–1909. The novelty of our approach is that we (a) recognise the similarity between the pattern of vertical motions and that of other normal faulting earthquakes, and (b) for the first time model the levelling data using the location and geometry of a well-known offshore capable fault. Our results indicate slip on the capable fault with a dip to the east of 70° and 5 m dip-slip at depth, with slip propagating to the surface on the sea bed. Our work emphasises that geological and geomorphological observations supporting maps of capable non-planar faults should not be ignored when attempting to identify the sources of major earthquakes.

Keywords: Eartquakes; Geology.

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Independent #confirmation of a #methane #spike on #Mars and a source region east of Gale Crater (Nat Geosci., abstract)

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

Article | Published: 01 April 2019

Independent confirmation of a methane spike on Mars and a source region east of Gale Crater

Marco Giuranna, Sébastien Viscardy, Frank Daerden, Lori Neary, Giuseppe Etiope, Dorothy Oehler, Vittorio Formisano, Alessandro Aronica, Paulina Wolkenberg, Shohei Aoki, Alejandro Cardesín-Moinelo, Julia Marín-Yaseli de la Parra, Donald Merritt & Marilena Amoroso

Nature Geoscience (2019)

 

Abstract

Reports of methane detection in the Martian atmosphere have been intensely debated. The presence of methane could enhance habitability and may even be a signature of life. However, no detection has been confirmed with independent measurements. Here, we report a firm detection of 15.5 ± 2.5 ppb by volume of methane in the Martian atmosphere above Gale Crater on 16 June 2013, by the Planetary Fourier Spectrometer onboard Mars Express, one day after the in situ observation of a methane spike by the Curiosity rover. Methane was not detected in other orbital passages. The detection uses improved observational geometry, as well as more sophisticated data treatment and analysis, and constitutes a contemporaneous, independent detection of methane. We perform ensemble simulations of the Martian atmosphere, using stochastic gas release scenarios to identify a potential source region east of Gale Crater. Our independent geological analysis also points to a source in this region, where faults of Aeolis Mensae may extend into proposed shallow ice of the Medusae Fossae Formation and episodically release gas trapped below or within the ice. Our identification of a probable release location will provide focus for future investigations into the origin of methane on Mars.

Keywords: Mars; Astrobiology; Geology; Methane; Space.

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#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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