Following the installation of a temporary seismological network in western Greece north of the Gulf of Patras, we determined the quality of the sites of each of the 10 stations in the network. For this, we used the horizontal-to-vertical spectral ratio (HVSR) method and calculated an average curve over randomly selected days between 0 Hz and 10 Hz. The daily HVSR curve is determined by the HVSR 12-hour calculation (one hour every two) without distinction between seismic ambient noise and earthquake signal. The HVSR curves obtained can be classified in three categories: flat curves without amplification, curves with a amplification peaks covering a large frequency range, and curves with one or more narrow peaks. In this third category C3, one station has one peak, two have two, and one has three. On the contrary of what it is commonly assumed, the amplitudes and the resonance frequencies of these narrow peaks are not stable over time in C3. We determined the maximum of the amplitude of each peak with the corresponding central frequency for each day during 2.5 years. Except for the station with three peaks, which finally appears stable within the uncertainties, the principal peak exhibits a seasonal variation, with a maximum in winter and a minimum in summer, the observations being more dispersed during winter. The second peak, when it exists, varies in the same way except at one station where it varies oppositely. These variations are clearly correlated with the loading and unloading cycle of the underlying aquifers as shown by the comparison with water level and yield measurements from wells located close to the stations. Moreover, they are also correlated with the vertical surface displacements observed at continuously recording GPS stations. The dispersion of the observed maximum amplitude in winter is probably related to the rainfall and the soil moisture modifying the S-wave velocity as revealed by other studies. From this study, we would like to emphasize that the use the HVSR method to constrain the S-wave velocity and the thickness of the sediment layer over the bedrock in the basin, has to be done with caution. Upon further confirmation of its robustness, the HVSR methodology presented here could be a good and easy-to-use tool for a qualitative survey of the aquifer backdrop and its seasonal behaviour, and of the soil moisture conditions.

The Aetolia-Akarnanian region, in Western Greece, is considered to be part of a micro-plate in formation, named the Ionian Island-Akarnanian Block (IAB), in the larger-scale Central Mediterranean tectonic context. The IAB accommodates the deformations between the surrounding tectonic structures that are the Corinth Gulf, the Hellenic subduction, the Kefalonia Transform Fault and the Apulian collision. This work presents the first results of a dense temporary seismic survey in the Aetolia-Akarnanian region (from the Amvrakikos Gulf to the Patras Gulf). Our local dense network has been designed in order to avoid gaps and to allow the recording of a major part of the Akarnania seismicity. With a semi-automatic events detection and picking program, we detected more than 15000 events from October 2015 to December 2018. With this important data set we constrained a 1D local velocity model. The comparison with the previous published models shows a possible significant velocity variation inside the region and especially at the Trichonis lake graben. Thanks to our data set and our velocity model, we precisely located 12723 seismic events with magnitude 0 < ML < 4.6, and a magnitude of completeness Mc = 1.0, that represents actually the most important catalogue for the Aetolia-Akarnania. Seismicity highlights specific seismic structures as clusters and a seismic plane below the West of Corinth Gulf that are briefly discussed.

&lt;p&gt;Characterized for the first time in 2013, the Island Akarnanian Block (IAB) is a micro-plate located in the western Greece. This micro-plate accommodates the deformation in between larger scale tectonic structures as the Gulf of Corinth (South-East), the Hellenic subduction (South) and the Apulian Collison (West).&lt;/p&gt;&lt;p&gt;&lt;span&gt;W&lt;/span&gt;&lt;span&gt;e &lt;/span&gt;&lt;span&gt;start&lt;/span&gt;&lt;span&gt;ed a micro-seismic &lt;/span&gt;&lt;span&gt;survey&lt;/span&gt;&lt;span&gt; (MADAM) at the end of 2015 with a dense seismological network &lt;/span&gt;&lt;span&gt;over the area, between the Gulf of Patras and the Gulf of Amvrakikos. &lt;/span&gt;&lt;span&gt;In order t&lt;/span&gt;&lt;span&gt;o obtain precise locations of the recorded events, we better constrained the local velocity model. In fact, &lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;everal velocity models &lt;/span&gt;&lt;span&gt;(local or regional) &lt;/span&gt;&lt;span&gt;have been proposed for this area. &lt;/span&gt;&lt;span&gt;H&lt;/span&gt;&lt;span&gt;owever,&lt;/span&gt;&lt;span&gt; the velocity model generally used by the scientific community remains the Hasslinger 98 velocity model. This model, nevertheless, raises some questions about its physical meaning, mainly due to a low velocity layer bet&lt;/span&gt;&lt;span&gt;w&lt;/span&gt;&lt;span&gt;ee&lt;/span&gt;&lt;span&gt;n &lt;/span&gt;&lt;span&gt;4 and 7 km-depth. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Thanks to our seismological network and permanent networks of the Corinth Rift Laboratory and the Hellenic Unified Seismic Network, w&lt;/span&gt;&lt;span&gt;e colle&lt;/span&gt;&lt;span&gt;c&lt;/span&gt;&lt;span&gt;ted and anal&lt;/span&gt;&lt;span&gt;y&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;ed&lt;/span&gt;&lt;span&gt; a huge quantity of data &lt;/span&gt;&lt;span&gt;a&lt;/span&gt;&lt;span&gt;c&lt;/span&gt;&lt;span&gt;quired &lt;/span&gt;&lt;span&gt;between &lt;/span&gt;&lt;span&gt;O&lt;/span&gt;&lt;span&gt;ctober 2015 and &lt;/span&gt;&lt;span&gt;D&lt;/span&gt;&lt;span&gt;ecember 2017. &lt;/span&gt;&lt;span&gt;Those analyses of &lt;/span&gt;&lt;span&gt;more than &lt;/span&gt;&lt;span&gt;10,000&lt;/span&gt;&lt;span&gt; events allowed us to &lt;/span&gt;&lt;span&gt;develop &lt;/span&gt;&lt;span&gt;a new &lt;/span&gt;&lt;span&gt;and robust &lt;/span&gt;&lt;span&gt;local velocity model, &lt;/span&gt;&lt;span&gt;wh&lt;/span&gt;&lt;span&gt;ich&lt;/span&gt;&lt;span&gt; is consi&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;tent with the seismic data and &lt;/span&gt;&lt;span&gt;the &lt;/span&gt;&lt;span&gt;geophysical obse&lt;/span&gt;&lt;span&gt;r&lt;/span&gt;&lt;span&gt;vations&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;The observed seismic activity is characterized by the presence of numerous clusters. The clusters are analysed in detail by relative relocations in order to appraise their physical processes and their possible implications in the fault activity to finally have a better understanding of the deformation mode(s) of the IAB micro-plate.&lt;/p&gt;