Seismic site characterization of the Kastelli (Kissamos) Basin in northwest Crete (Greece): Assessments using ambient noise recordings

Crete is actively seismic and site response studies are needed for estimating local site conditions subjected to seismic activity. In order to collect basic data, we performed ambient noise recordings to estimate the site response of the surface and near subsurface structure of the small-scale Kastelli Basin in northwest Crete. The spatial horizontal to vertical spectral ratios (HVSR) resonance pattern of the investigated sites in the centre of the Basin consists of either one or two peaks divided into low to high frequency range in different sites as follows: (a) in some sites only one amplified peak at low frequencies (0.6–1.2 Hz), (b) in other sites only one amplified peak at medium frequencies (2.9–8.5 Hz) and (c) in yet other sites two amplified peaks in the low to high frequency range (0.6–15.5 Hz). The investigated sites are amplified in the frequency range 0.6–15.5 Hz, while the amplitude reaches to a factor of 4 in the spectral ratios. The one HVSR amplified peak at low frequencies is related to locally soft or thick Quaternary deposits. Microtremors were measured in the coastal northwest part of the Basin in a well—lithified Cretaceous limestone site characterized by fractures and faults striking predominantly in a sector NNE to NNW. Sites of one amplified peak at medium frequencies are extended from coastal northwest to southwest delineating a structure striking to NNW. The two amplified peaks are attributed to shallow subsurface heterogeneities/irregularities, locally induced by fault zones and to the overlying Quaternary deposits. Spatial HVSR variations in the frequency and HVSR shape delineate four structures striking NNE, NNW and in a sector NW to WNW, crosscutting the dense populated Basin suggesting that microtremors could be a valuable tool for providing a first approximation of fault zone delineation at least for the Kastelli-Kissamos Basin. The Basin is classified into the X soil category of the Greek Seismic Code 2000.This work was implemented through the project entitled “Interdisciplinary Multi-Scale Research of Earth-quake Physics and Seismotectonics at the Front of the Hellenic Arc (IMPACT-ARC)” in the framework of action “ARCHIMEDES III—Support of Research Teams at TEI of Crete” (MIS380353) of the Operational Program “Education and Lifelong Learning” and is co-financed by the European Union (European Social Fund) and Greek national fund

A probability electrical resistivity tomography imaging of complex tectonic features in the kissamos and paleohora urban areas, western crete (Greece)

A number of 2D Electrical Resistivity Tomographies (ERT) was conducted in northwest and southwest Crete with the aim to model geotectonic features at selected urban sites. The study area is located within the central forearc of the Hellenic subduction zone. Thirteen ERT profiles were realized using the dipole-dipole electrode and/or the Wenner-Schlumberger arrays. In order to model the resistivity distribution, the probability-based electrical resistivity tomography inversion (PERTI) method has been applied. The main features of the PERTI method are: (i) unnecessity of a priori information; (ii) full, unconstrained adaptability to any kind of dataset, including the case of non-flat topography; (iii) independence from data acquisition techniques and spatial regularity; (iv) capability to resolve complex continuous resistivity variation. Since the present case-study is the first application of the PERTI algorithm to locate fault zones and near subsurface irregularities, its routine has been tested using the well-known RES2DINV commercial software as reference. The comparison has shown a common coherence between the results of the two inversion methods and confirmed the better filtering capacity and greater versatility of the PERTI algorithm, already outlined in a number of previous papers dealing with archaeological applications. © 2019, Editrice Compositori s.r.l.. All rights reserved