ALBERT

Description: The deformation of the eastern Corinth rift (Greece) is distributed along several E-W trending active normal faults. Here the 25-km-long Pisia fault experienced up to 150 cm of coseismic displacement during the 1981 Alkyonides earthquake sequence (M = 6.7, 6.4, 6.3). Using terrestrial laser scanning, coupled with analyses of color changes, lichen colonization, and karstic features, we identify differentially weathered horizontal stripes on the exposed Pisia fault plane. The stripe boundaries occur at scarp heights of 1.10, 2.05, 2.85, 3.60, 4.15, and 5.15 m, with two additional possible boundaries at 3.10 and 4.65 m (~±0.1 m, respectively). This indicates that six to eight paleoearthquakes have exhumed the fault plane in a series of distinct coseismic slip events. A vertical profile of cosmogenic 36Cl measurements is used to constrain age models of the exhumation. The results imply that, in addition to the last earthquake of 1981 (EQ1), exhumation events occurred at ~2.0 kyr (EQ2), ~3.1 kyr (EQ3), ~4.5 kyr (EQ4/4a,b), ~6.0 kyr (EQ5), and ~7.3 kyr (EQ6/6a,b), with modeled age uncertainties of ~0.7 kyr. Bayesian modeling provides a middle and late Holocene slip rate of 0.5–0.6 mm/yr (last 7.3 ± 0.7 kyr), while the upper part of the 8.45-m-high fault plane was exhumed at a higher rate of 0.8–2.3 mm/yr (7.3 ± 0.7 kyr to 10.2 ± 1.9 kyr). This slip rate variability suggests an increased seismicity or larger slip events during the early Holocene. ©2018. American Geophysical Union. All Rights Reserved.

Description: Many active normal faults throughout the Aegean juxtapose footwall limestone against hanging-wall colluvium. In places, this colluvium becomes cemented and forms large hanging-wall lobes or sheets of varying thickness attached to the bedrock fault. Investigations at the Lastros Fault in eastern Crete allow us to define criteria to distinguish between cemented colluvium and fault cataclasite (tectonic breccia), which is often present at bedrock faults. Macro- and microscopic descriptions of the cemented colluvium show that the colluvium was originally deposited through both rockfalls and debris flows. Stable isotope analyses of oxygen and carbon from 83 samples indicate that cementation then occurred through meteoric fluid flow in the fault zone from springs at localised positions along strike. Palaeotemperature calculations of the parent water from which the calcite cement precipitated are indicative of a climate between 7°C and 10°C colder than Crete’s present average annual temperature. This most likely represents the transition between a glacial and interglacial period in the late Pleistocene. Ground-penetrating radar also indicates that cemented colluvium is present in the hanging-wall subsurface below uncemented colluvium. Using these results, a model for the temporal development of the fault and formation of the cemented colluvium is proposed.

Description: Two normal faults on the island of Crete and mainland Greece were studied to test an innovative workflow with the goal of obtaining a more objective palaeoseismic trench log, and a 3-D view of the sedimentary architecture within the trench walls. Sedimentary feature geometries in palaeoseismic trenches are related to palaeoearthquake magnitudes which are used in seismic hazard assessments. If the geometry of these sedimentary features can be more representatively measured, seismic hazard assessments can be improved. In this study more representative measurements of sedimentary features are achieved by combining classical palaeoseismic trenching techniques with multispectral approaches. A conventional trench log was firstly compared to results of ISO (iterative self-organising) cluster analysis of a true colour photomosaic representing the spectrum of visible light. Photomosaic acquisition disadvantages (e.g. illumination) were addressed by complementing the data set with active near-infrared backscatter signal image from t-LiDAR measurements. The multispectral analysis shows that distinct layers can be identified and it compares well with the conventional trench log. According to this, a distinction of adjacent stratigraphic units was enabled by their particular multispectral composition signature. Based on the trench log, a 3-D interpretation of attached 2-D ground-penetrating radar (GPR) profiles collected on the vertical trench wall was then possible. This is highly beneficial for measuring representative layer thicknesses, displacements, and geometries at depth within the trench wall. Thus, misinterpretation due to cutting effects is minimised. This manuscript combines multiparametric approaches and shows (i) how a 3-D visualisation of palaeoseismic trench stratigraphy and logging can be accomplished by combining t-LiDAR and GPR techniques, and (ii) how a multispectral digital analysis can offer additional advantages to interpret palaeoseismic and stratigraphic data. The multispectral data sets are stored allowing unbiased input for future (re)investigations.