Seafloor acoustic ranging data across the North-Anatolian Fault, Marmara Sea, Turkey
|Temporal extent||2014-10-29 -2018-01-29|
|Author(s)||Royer Jean-Yves1, Piété Helen1, Ballu Valérie2, Sakic Pierre2|
|Affiliation(s)||1 : CNRS & Université de Brest, Laboratoire Géosciences Océan IUEM rue Dumont d’Urville, 29280 Plouzané
2 : CNRS & Université de La Rochelle, Laboratoire Littoral Environnement et Sociétés La Rochelle
In October 2014, a ranging network of 10 acoustic transponders was installed across an active segment of the North-Anatolian Fault, in the Marmara Sea at a depth of about 800 m, for up to 5 years (Figure 1). This active fault segment is lacking any major seismic activity since the 18th century. The purpose of this acoustic ranging experiment was to determine whether this fault is continuously and aseismically creeping (i.e. slipping) or is locked and thus accumulating stress that could cause a large magnitude earthquake, few ten kilometers away from Istanbul.
The acoustic network comprised 4 transponders from the University of Brest, France, and 6 transponders from the Geomar Institute, Germany. The data available through this web site corresponds to the data collected by the 4 French stations only. They include sets of acoustic ranging between pairs of stations (i.e. two-way-travel times), in addition to sound-speed, temperature and pressure measurements at each station. The sampling rate varies with the data type, but is generally hourly (one or several samples every hour). These are the raw, unprocessed data. For instance, distances must be inferred from the two-way-travel times and sound-speeds.
The experiment lasted until January 2018.
More information about the acoustic network can be found in the paper by Sakic et al. (2016; see reference below).
|Utilisation||Data are published without any warranty, express or implied. The user assumes all risk arising from his/her use of data. Data are intended to be research-quality and include estimates of data quality and accuracy, but it is possible that these estimates or the data themselves contain errors. It is the sole responsibility of the user to assess if the data are appropriate for his/her use, and to interpret the data, data quality, and data accuracy accordingly. Authors welcome users to ask questions and report problems.|
|Acknowledgements||The authors wish to thank the Captains and crews of RV Pourquoi Pas?, RV Poseidon, and RV Yunus for the successful deployment of the instruments (MARSITE Cruise in 2014) and recovery of the data (cruises POS484 in 2015, POS497 in 2016, YUNUS17 in 2017 and YUNUS18 in 2018) respectively. The deployment cruise was organized in the framework of the European FP7 Marsite project. This experiment received support from Labex Mer in Brest (ANR 10-LABX-19), from the French component (INSU-CNRS) of the EMSO European research infrastructure, and from the collaborative ANR/TUBITAK project MAREGAMI (ANR 16-CE03-0010 and Tübitak Project 116Y371). The acoustic equipment (transponders, modem) was funded by Région Bretagne (CPER ODO 2007-2015). This work is dedicated to the memory of the Principal Investigator of this subsea geodetic project, Dr. Anne Deschamps, who passed away shortly after leading the successful deployment of the acoustic transponders.|
Acoustic transponders are Sonardyne Fetch-AMT. The acoustic ranging signal is a medium –frequency (22.5 kHz), phase – coded 8 ms – long pulse. Observations are time stamped by a precision clock with a 1 µs accuracy, and a drift < 3 ppm in 10 years. The processor of the transponder performs the cross-correlation between transmitted and received signals. The instrument is equipped with additional sensors: a probe measuring the speed of sound in seawater, pressure and temperature sensors and an inclinometer.
Transponders are programmed to perform multiple, redundant, high frequency measurements in a slave/master mode, based on the following sequence: every hour, each unit wakes up as “master”, performs measurements with each of its additional sensors, and interrogates simultaneously the other units of the array. The solicited “slave” transponders subsequently answer with an identical signal, and simultaneously measure the temperature and sound speed in seawater.