Small earthquakes caused by migrating gasses in the underground

Seismic data in the Istanbul-Marmara region show: Earthquakes carry out degassing, which can then cause further shocks.

The metropolitan area of Istanbul with around 15 million inhabitants is considered to be particularly earthquake-prone. In order to be able to assess the risk correctly, researchers must decipher the processes underground. Now further progress has been made by an international team, to which Marco Bohnhoff from the GFZ German Research Center for Geosciences belongs. Below the Marmara Sea, they detected earthquakes that were not directly caused by tectonic stresses but by rising natural gas. Their findings are published in the journal Scientific Reports.

The team led by Louis Geli of the French Research Center Ifremer analyzed seismic data recorded after an earthquake in the Western part of the Maramara Sea on 25 July 2011 with a magnitude of 5.1. As expected, several aftershocks occurred in the following days and weeks, but they were less severe. "A stronger earthquake changes the stress in the underground. This results in further shocks - so-called aftershocks - in which the stress changes are then compensated again," explains Bohnhoff. This happened in the summer of 2011 below the Marmara Sea near Istanbul. It was striking, however, that only a few aftershocks occurred in the crystalline basement where the main earthquake had its origin. "Instead, we recorded a lot of tremors at very shallow depths below the seafloor," says Bohnhoff who was involved in the localization and analysis of the shallow quakes. "This was quite surprising, because these layers consist of soft sediment that typically deforms aseismically under tectonic stress and does not make abrupt movements typical for earthquakes."

In fact, there is another underlying mechanism, as the authors explain: The M5.1 earthquake has disrupted the stress field like striking a bell so that a natural gas reservoir in close proximity to the tectonic disturbance has come under increased pressure. As a result, gas escaped and moved upwards where it triggered weaker earthquakes. Different processes come into question. Small shear fractures may have been activated, or the outgassing may have caused oscillations of water-filled cavities, a process also known from volcanoes or gas leaks. "The exact processes taking place below the bottom of the Maramara Sea can not be resolved from the available data", says the geophysicist. This requires seismometers, which are installed even closer to the source locaction, for example in boreholes. These were missing – yet.

Bohnhoff and his colleagues from the GFZ and other international partner institutes have set up such downhole instrumentation further east in the greater Istanbul area as part of the GONAF observatory (Geophysical Observatory at the North Anatolian Fault). They are designed to detect the ongoing deformation of the tectonic plates, tensions in the Earth's crust and vibrations very accurately and thus ultimately allow for a more realistic risk analysis for the upcoming strong earthquake at the gates of the mega-city. Basically, there the probability for a magnitude 7 or larger earthquake by the year 2040 is 35 to 70 percent.

"The seismic hazard and risk for the metropolitan region of Istanbul does not necessarily change as a result of the new findings. But they must be included in various earthquake scenarios to make them more realistic," says Bohnhoff. "In this way, we also highlight an aspect hitherto completely ignored by the public, i.e. that the spatial proximity of the North Anatolian Fault Zone and the gas deposit poses an additional hazard potential." Due to the deposit large gas tanks are located at a short distance on land. In the case of a strong earthquake, there is an increased risk of explosion or gas leaks. Bohnhoff: "Such hazards increase the risk to the population of being damaged as a result of an earthquake."

Original study: L. Géli et al., 2018. Gas and seismicity within the Istanbul seismic gap. Scientific Reports. DOI: 10.1038/s41598-018-23536-7

Additional News

Portrait Lars Bernard, green background

The Board of Trustees appoints Prof. Lars Bernard to the Scientific Advisory Board of the…

Portrait photo of Harald Schuh, background: green

AGU Award for Harald Schuh

The glass building with flagging "IASS" at Helmholtzstraße 5.

An ideal addition to the Helmholtz Association

SLR Station, Laser

New DFG Research Unit “Clock Metrology: A Novel Approach to TIME in Geodesy” with GFZ…

Niels Hovius portrait

Niels Hovius appointed to the renowned "National Academy of Science and Engineering –…

[Translate to English:] GFZ-Logo

GFZ's position on the Leopoldina paper “Earth System Science”

Kimberella fossile

Feeding strategies of the oldest known animals (Ediacara)

Portraits of the five young researchers

EGU OSPP Awards 2022 to five GFZ researchers

[Translate to English:] Lila Flagge wehend über einem Dachgiebel

Interviews on the occasion of the Purple Light Up 2022

Obituary picture of Dr. Kemâl Erbas.

Obituary Dr. Kemâl Erbas

Two profile photos and in between the logo of BMWK and a symbol image for a text document.

Important signal for the expansion of deep geothermal energy

German map with quality-checked data points, shown as columns

A new heat-flow analysis shows higher values for Germany

P. Martinez-Garzon in a forest next to a giant split rock

Dr. Patricia Martinez-Garzon wins ERC Starting Grant for her project QUAKE-HUNTER

Map of Türkiye with the marked epicentre of the earthquake in the northwestern part of the country

Background on today's earthquake in northwest Türkiye

Topography map of the alps.

What is driving the Alps upwards?

Groupp picture ICDP/IODP Kolloquiums

Joint IODP/ICDP-Colloquium at GFZ

Teachers in lecture hall during lecture

"Extreme Events in the Earth System" - 20th "System Earth" Autumn School

Two young researchers stand in front of trees holding their certificates, next to them stands Ludwig Stroink, who awarded the certificates.

“GFZ Friends” honours Theresa Hennig and Lei Wang with the “Friedrich-Robert-Helmert Prize…

Satellite image of a desert area: Colorful spots show different minerals.

German environmental satellite EnMAP: start into regular operation

On the left, a measuring tower in a low overgrown tundra landscape.

More methane from Siberia in summer

[Translate to English:] Profilfoto mit schwarzem Rahmen von Henning Francke

Obituary: Henning Francke

Group photo with projekt responsible

Making geodata interoperable and suited for curiosity driven research: GEO-INQUIRE project…

Schema Energiebereitstellung durch Geothermie

European Geothermal Congress from 17 to 21 October 2022 in Berlin

Gruppenfoto PAM

International Conference on Polar and Alpine Microbiology

Leni Scheck Wenderoth

“AWG Professional Excellence Award” for Magdalena Scheck-Wenderoth

Ausbildung am GFZ

Berufsausbildung und duales Studium am GFZ

Dr. Ute Weckmann during the opening speech of the workshop

Dr. Ute Weckmann takes over the chairmanship of IAGA Division VI

Anke Neumann aon a boat during a research trip

Dr Anke Neumann is a Senior Humboldt Research Fellow

Earth Model

New DFG priority programme on deep Earth evolution over geologic time

Logo of the Helmholtz Innovation Labs: written words only

Successful interim evaluation of the two Helmholtz Innovation Labs at the GFZ

back to top of main content