Are foreshocks a systematic indicator for upcoming earthquakes?

New findings from Istanbul raise hope that preceding signs of massive earthquakes can be detected.

The 16-million population center of Istanbul is facing a tremendous seismic hazard and risk due a pending major earthquake along the North Anatolian Fault below the Sea of Marmara. This fault is a major plate boundary that crosses northern Turkey from east to west, and that produced several destructive earthquakes during the 20th century. The series of large earthquakes included an event in Erzincan in eastern Turkey in 1939. Since then, the subsequent earthquakes moved steadily westwards reaching the Marmara region in 1999. The only portion of the entire plate-bounding fault that did not break since 1766 is the segment below the Sea of Marmara immediately to the south of Istanbul. There, a large earthquake with magnitude M larger than 7 is overdue and might occur anytime. Yet, in September 2019, a sequence of two nearly collocated moderate earthquakes (M4.7 and M5.8) occurred in the center of this hazardous fault portion. These two events were largely felt in Istanbul, and reminded people of the possibility of a large earthquake hitting the megalopolis.

The GFZ Potsdam has a research focus in the broader Istanbul region and recently implemented the geophysical observatory GONAF (www.gonaf-network.org) to study ongoing tectonic processes with unprecedented detail. Using seismometer recordings from regional seismic networks and in particular from GONAF, it was possible to detect small earthquakes that were accompanying the two mainshocks. The analysis of these small events revealed that the September 2019 earthquakes were preceded by a number of foreshocks. While some of them are distributed along the whole length of the fault segment, others were concentrating around the nucleation point of the two larger earthquakes. These observations suggest that a preparation process occurred during the two days preceding each earthquake. Furthermore, this process was accelerated during the hours preceding the earthquakes leading to the larger events. During the days preceding the earthquakes, the entire final rupture length of the rupture was illuminated by small earthquakes. This raises the question of the existence of a link between the size of the foreshock-activated region and the final magnitude of the mainshock.

While observations of foreshocks preceding large earthquakes like the tsunami-generating Tohoku/Japan M9 2011 and Iquique/Chile M8.1 2014 earthquakes are now common, this study reports equivalent observations of small seismicity preceding moderate earthquakes. “These observations support the hypothesis that earthquakes are not a completely random process and that they are preceded by a detectable preparation phase lasting from several hours to several days”, says Dr. Virginie Durand, lead author of the study. Therefore, these results are encouraging to complement existing early-warning systems that can ultimately lead to an extended warning time for people.

The study was performed as part of the Young Investigators Group SAIDAN led by Dr. Patricia Martínez-Garzón, who says that “this type of observations may serve to improve operational earthquake forecasting systems, provided the existence of densified seismic monitoring networks near active faults, like the GONAF in the Istanbul region, and of near-real time processing of earthquake recordings.”

Original study: A Two-Scale Preparation Phase Preceded an M w 5.8 Earthquake in the Sea of Marmara Offshore Istanbul, Turkey, Durand, V., S. Bentz, G. Kwiatek, G. Dresen, C. Wollin, O. Heidbach, P. Martínez-Garzòn, F. Cotton, M. Nurlu, and M. Bohnhoff (2020). , Seismol. Res. Lett., 1–9, doi: 10.1785/0220200110

Scientific contact (English / French):
Dr. Virginie Durand
Scientist at GFZ Section 4.2 Geomechanics and Scientific Drilling
Helmholtz Centre Potsdam
German Research Centre for Geosciences GFZ
Telegrafenberg
14473 Potsdam
e-mail: virginie.durand@gfz-potsdam.de
phone: +49 331 288-27502

Scientific contact (English / German):
Prof. Dr. Marco Bohnhoff
Head of GFZ Section 4.2 Geomechanics and Scientific Drilling
Professor of Experimental and Borehole Seismology at Free University Berlin
Executive Director of the International Continental Scientific Drilling Program
Helmholtz Centre Potsdam
German Research Centre for Geosciences GFZ
Telegrafenberg
14473 Potsdam
e-mail: bohnhoff@gfz-potsdam.de
phone: +49 331 2881327

Media contact:
Josef Zens
Head of Public and Media Relations
Helmholtz Centre Potsdam
German Research Centre for Geosciences GFZ
Telegrafenberg
14473 Potsdam
e-mail: josef.zens@gfz-potsdam.de
phone: +49-331-288-1040

Additional News

Logo of the Helmholtz Innovation Labs: written words only

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

Schematic of plunging Earth plates under the ocean with water transport and the Al molecules involved: This is how water migrates deeper into the Earth than previously assumed.

Water is seeping deeper into Earth than expected

From the air, a view of Istanbul, a city of millions, and the surrounding sea.

"Earthquakes don’t occur out of nowhere"

Group photo with all the people who attended the farewell

Honouring Prof. Onno Oncken with a scientific colloquium

DEUQUA Logo mit Mammut und Friedenstaube

DEUQUA 2022 Tagung am GFZ

PAW Logo

Postdoc Appreciation Week Germany

Building, photo taken in winter, Isaac Newton Institute

Simons Scholarship for Dr Monika Korte

Die Verteilung der seismischen Stationen auf einer Karte der Region.

How deeply does Eifel volcanism sleep?

Geomagnetic Field. Space with stars, Earth with animation around

GFZ film among the finalists of the Earth Futures Festival 2022

Earth's radiation belt: High-energy particles modelled around the Earth. The particles are ring-shaped

A new population of particles in the Earth’s radiation belts

[Translate to English:] Die teilnehmenden GFZ Mitarbeiter als Gruppenfoto

2nd proWissen run in Potsdam with successful participation by GFZ employees

The group on the first day of work.

New faces at the GFZ - start of the training year 2022/2023

Forest vs no forest on two sides of a road

Agriculture drives more than 90% of tropical deforestation

Group photo: people on the roof terrace of a house

2nd International Symposium of International Association of Geodesy’s Commission 4…

[Translate to English:] Foto eines Bergs mit darüber gelegter Skizze des geologischen Profils.

How thick should clay be as a host rock for a repository?

White dots of different thicknesses in a hexagonal pattern on a black ground.

Synthesis of hexagonal SiGe semiconductor using high pressure and temperature

Landslide on a slope directly adjacent to a settlement with small houses.

Landslides increasingly threaten the world's urban poor cities

Different coloured liquids mix in an aquarium. A child watches.

Catching up after Corona: "GEOtogether" brings joy for pupils in collaborative…

A woman and a man stand on a stage holding a picture with a coloured map of Türkiye..

Four decades of joint Turkish-German earthquake research

Egon Althaus sitting around a table with colleagues outside on a project

We mourn the death of Egon Althaus (1933-2022)

A dry dam near Capetown, South Africa.

The challenge of unprecedented floods and droughts in risk management

Drawing of a fictional historical submersible.

Eleven short research stays with GFZ participation funded

Drilling platform on Lake Junin with several people on it

Tropical glaciers followed the rhythm of the ice sheet expansion in the northern…

Schematic representation of the VECTOR project: A large arrow with different levels - from the earth's surface to underground.

Improving the exploration efficiency in Europe

Hoby Razafindrakoto

Project from Dr. Razafindrakoto to create a seismological lab in Madagascar wins ARISE…

3D digital Earth at night

Open-Earth-Monitor getting started

The dam of the Steinbach Dam in the Eifel region, cut by flooding but not destroyed.

Flood risk management after the Eifel flood in July 2021

Group picture of the Cermak7 Conference in front of the Museum Barberini in Potsdam

International heat flow conference and workshop in Potsdam

Castor platform in the ocean. The sea is still.

Filling geological gas reservoirs: Causal research in the most important event of induced…

People sit on chairs in a circle in a room.

GFZ PhD Days

back to top of main content