The PZN-P6 pressure increases over a period greater than 3.5 months starting around 1 week after the 2013EQ. The vertical displacement at TEKR also indicates a perturbation of the trend between 2013EQ and 2014EQ.Įxcess pore-pressure data (i.e., above hydrostatic) measured at 7.08 mbsf (PZN-P6) and 6.28 mbsf (PZS-P5) show two opposite trends (Fig. Figure 2 shows a decomposition plot of TEKR geodetic data with a trend of the northern displacement (with respect to fixed EU plate) strongly affected by the 2013EQ. For the present study, we used the STL (seasonal-trend decomposition based on LOESS) 29 procedure in R 30, which is a filtering procedure that decomposes a time series into three components: trend, seasonal, and remainder parts. In a previous study, an accuracy analysis of relative positions of permanent GPS stations in the Marmara Region has shown that the root mean square error is within 1 mm for the north–south, east–west components while it is between 2 and 3 mm for the up–down direction 16. The accuracy of an observed position in the north–south, east–west, and in up–down directions depends significantly on the duration of the observing period and on the accuracy of the GPS satellite orbits used during processing 28. For this last case, the plate motion trends are removed for the horizontal component time series. GPS time series data are provided in the IGS14 27 reference frame and in the plate fixed reference frame by considering the plate on which the station lies. In parallel, we analyze 7-year period GPS data 26 using publicly available data from Nevada Geodetic Laboratory-NGL ( ). The PZS and PZN water depths are 667 and 672 m, respectively.ĭuring the monitoring period, two notable earthquakes occurred at epicentral distances from PZN of 12.5 24 and 209 km 25, respectively: the 11 km deep, Mw 4.8 (2013EQ) nucleated along the MMF in the area where repeating earthquakes have been documented, while the 9 km deep, Mw 6.9 earthquake (2014EQ) struck the Ganos segment of the NAF in the Thracian Sea (epicenters in Fig. 1), to investigate the coupling between the hydrogeological and tectonic systems along the WH segment of the MMF. ![]() In this context, two differential piezometers 22 measuring pore pressures in excess of hydrostatic pressures (“Methods”) were deployed from Oct 2013 to Nov 2014 23 within the MMF valley and close to the MV, respectively (PZS and PZN in Fig. The largest gas emissions along the MMF were found to occur within a 900 m to 1000 m zone on either side of the MMF 20, which encompassed the MV and have been interpreted as being the trace of a high-permeability damage zone 21. 1A), where active seeps 17, 18, 19 were found in association with an active mud volcano (MV) located <1 km away from the MMF trace (Fig. Based on submarine, acoustic ranging data, aseismic creep rates of 9–16 mm/year 16 were measured in the Western High area (WH in Fig. The common occurrence of small repeating earthquakes 14 suggests that the MMF has a deep creep component in the western Sea of Marmara, but not in the central nor in the eastern segments 15. The western segments of the MMF are characterized by a higher level of background seismicity compared to the eastern segments. ![]() 1A)-taking 75% of the right-lateral geodetic slip rate (~20 mm/year) between the Eurasian Plate and the Anatolian block 10, 11, 12, 13. Studies have now largely converged to a scheme with a master fault-the Main Marmara Fault 10 (MMF red line in Fig. ![]() The Sea of Marmara-south of Istanbul-has become, after 20 years of investigations, one of the most well-known submarine domains on earth. Slow slip events (SSEs) have mostly been studied using on-shore Global Positioning System (GPS) data 6, where the discovery of fluid flow based on direct, in situ observations from the seafloor along the subducting plate interfaces have led to the hypothesis of a causal relationship between SSEs and changes in fluid activities at the fault zone 7, 8, 9. While the major role and influence of pore pressure has long been proposed 3, 4, 5, it has never been observed because of the difficulty in linking deep processes at seismogenic depths with near-surface pore-pressure measurements. That tectonic plates may slip slowly and episodically along segments of their boundaries is one of the most intriguing, unexplained observations in solid earth geophysics, as it reveals a continuum of transient deformation along active faults, ranging from seismic rupture to aseismic events 1, 2.
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