A new seismic tomography of Aigion area (Gulf of Corinth, Greece) from the 1991 data set

Abstract

S U M M A R YA new three-dimensional delay traveltime tomography is performed to image the intermediate structure of the western Gulf of Corinth. A large data set, collected in 1991 during a two-month passive tomographic experiment, has been reanalysed for the reconstruction of detailed Vp and Vs images. An improved tomography method, based on an accurate traveltime computation, is applied to invert simultaneously delayed P and S first-arrival traveltimes for both velocity and hypocentre parameters. We perform different synthetic tests to analyse the sensitivity of tomography results to the model parametrization and to the starting 1-D model selection. The analysis of the retrieved Vp and Vs models as well as deduced Vp/Vs and Vp · Vs images allows us to interpret and delineate the distribution of lithological variation, porosity/crack content and fluid saturation in the upper 9-11 km of the crust beneath the gulf. The tomographic models image a rather complex crustal structure, which is characterized by a vertical change in both velocity features and seismicity distribution. We identify a shallower zone of the crust (0-5 km depth), in which velocity distributions seem to be controlled by the still active N-S extensional regime and a deeper zone (7-11 km depth), which matches the seismogenic zone. The correlation between this latter and a specific unit of the Hellenic mountain structure (the Pyllite-Quartzite series) allows us to suggest a possible explanation for seismicity concentration in a narrow band at 7-9 km depth. Finally, the occurrence of clusters showing low-angle normal fault mechanisms in areas characterized by high Vp/Vs values indicates a possible role of fluids in triggering brittle creep along the identified low-angle normal faults.

A New Passive Tomography of the Aigion Area (Gulf of Corinth, Greece) from the 2002 Data Set

“…This data set has been used as well to perform tomographic studies. First results were obtained by LE MEUR et al (1997) and new velocity models were constructed by LATORRE et al (2004b) using an improved tomographic technique. LATORRE et al (2004b) found a two-layer vertical structure and the presence of a high Vp/Vs anomaly at depth, suggesting a possible role of fluids in the rifting process.…”

“…First results were obtained by LE MEUR et al (1997) and new velocity models were constructed by LATORRE et al (2004b) using an improved tomographic technique. LATORRE et al (2004b) found a two-layer vertical structure and the presence of a high Vp/Vs anomaly at depth, suggesting a possible role of fluids in the rifting process. Despite important results, the quality of the 1991 data is limited because of many vertical single component (1C) stations, imposing a major limitation in constraining the mid-crust structure and the seismicity distribution.…”

Relocation of recent seismicity and seismotectonic properties in the Gulf of Corinth (Greece)

“…Several attempts to record the intense microseismicity in the study area were made in the past three decades. In 1991, a local network consisted of 51 seismological stations was installed in the western Corinth Gulf and operated for two months (Rigo et al 1996;Latorre et al 2004). During the summer of 1993, a temporary seismological network was installed over a period of seven weeks around the eastern Corinth Gulf (Hatzfeld et al 2000).…”

Absolute earthquake locations using 3-D versus 1-D velocity models below a local seismic network: example from the Pyrenees

“…The code developed by Monteiller (2005) has been already applied in several studies (Latorre et al 2004;Vanorio et al 2005;Gautier et al 2006;Theunissen et al 2012b). It is a linearized, iterative and damped least-square approach.…”