Two normal faults on the island of Crete and mainland Greece were studied to test an innovative w... more 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 palaeo-seismic 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 mul-tiparametric approaches and shows (i) how a 3-D visualisa-tion 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.
The majority of normal faults on Crete comprise Mesozoic carbonate bedrock fault scarps juxtapose... more The majority of normal faults on Crete comprise Mesozoic carbonate bedrock fault scarps juxtaposed against Quaternary alluvial-colluvial sediments. An outcrop at the west dipping Sfaka fault in the east of the island was studied by combining classical paleoseismic trenching techniques and multispectral approaches. A conventional trench log was compared to results of iso cluster analyses of both a true color photomosaic representing the spectrum of visible light and a near-infrared backscatter signal image from t-LiDAR measurements. The disadvantages of passive data collection (e.g. illumination) were thus negated by complementing the dataset with active t-LiDAR measurements. The multispectral analysis of distinct layers corresponds well with the experience-based conventional trench logging. Based on this, a 3D-interpretation of GPR data collected on the vertical trench wall was possible. This allows layer thicknesses and subsurface geometries to be estimated.
Corinth Gulf is one of the fastest expanding regions worldwide, influenced by several major norma... more Corinth Gulf is one of the fastest expanding regions worldwide, influenced by several major normal faults. We measured the magnetic susceptibility within boreholes, drilled at the footwall and hanging-wall of the Kalamaki fault, a secondary structure that intersects the Corinth Canal. We correlate magnetic susceptibility (MS) measurements with paleoenvironmental and lithological alternations within the boreholes. We have ascribed low MS values to marine highstand deposits and high MS values to lowstand terrestrial deposits. Glacioeustatic sea level changes and tectonic movements have led to a very complicated lithosedimentary pattern, and magnetic susceptibility (MS) measurements can help us interpret the fault's activity.
We present the preliminary results from a multi-method investigation on the Lastros-Sfaka Graben ... more We present the preliminary results from a multi-method investigation on the Lastros-Sfaka Graben located in the Ierapetra Fault Zone in eastern Crete. We scanned c. 1.2 km of the Lastros Fault with t-LiDAR and identified areas for throw rate calculations at locations with no external influences (anthropogenic or erosional). Preliminary maximum throw rates are 0.7 mm/yr, which is significantly less than stated in the literature. Cemented colluvium is located on the Lastros Fault, forming hanging-wall talus lobes and sheets of varying thickness attached to the fault plane. The cement is formed of calcite and further laboratory analyses are underway to determine its formation processes. GPR has been undertaken at the Lastros Fault and cemented colluvium is also present within the hanging-wall subsurface. Road cut (trenching) investigations on the Sfaka Fault identified fill material most likely deposited soon after the last paleoearthquake(s) that occurred on the fault; 14 C dating is ...
Corinth Gulf is one of the fastest expanding regions worldwide, influenced by several major norma... more Corinth Gulf is one of the fastest expanding regions worldwide, influenced by several major normal faults. We measured the magnetic susceptibility within boreholes, drilled at the footwall and hanging-wall of the Kalamaki fault, a secondary structure that intersects the Corinth Canal. We correlate magnetic susceptibility (MS) measurements with paleoenvironmental and lithological alternations within the boreholes. We have ascribed low MS values to marine highstand deposits and high MS values to lowstand terrestrial deposits. Glacioeustatic sea level changes and tectonic movements have led to a very complicated lithosedimentary pattern, and magnetic susceptibility (MS) measurements can help us interpret the fault's activity.
We present the preliminary results from a multi-method investigation on the Lastros-Sfaka Graben ... more We present the preliminary results from a multi-method investigation on the Lastros-Sfaka Graben located in the Ierapetra Fault Zone in eastern Crete. We scanned c. 1.2 km of the Lastros Fault with t-LiDAR and identified areas for throw rate calculations at locations with no external influences (anthropogenic or erosional). Preliminary maximum throw rates are 0.7 mm/yr, which is significantly less than stated in the literature. Cemented colluvium is located on the Lastros Fault, forming hanging-wall talus lobes and sheets of varying thickness attached to the fault plane. The cement is formed of calcite and further laboratory analyses are underway to determine its formation processes. GPR has been undertaken at the Lastros Fault and cemented colluvium is also present within the hanging-wall subsurface. Road cut (trenching) investigations on the Sfaka Fault identified fill material most likely deposited soon after the last paleoearthquake(s) that occurred on the fault; 14 C dating is ...
The majority of normal faults on Crete comprise Mesozoic carbonate bedrock fault scarps juxtapose... more The majority of normal faults on Crete comprise Mesozoic carbonate bedrock fault scarps juxtaposed against Quaternary alluvial-colluvial sediments. An outcrop at the west dipping Sfaka fault in the east of the island was studied by combining classical paleoseismic trenching techniques and multispectral approaches. A conventional trench log was compared to results of iso cluster analyses of both a true color photomosaic representing the spectrum of visible light and a near-infrared backscatter signal image from t-LiDAR measurements. The disadvantages of passive data collection (e.g. illumination) were thus negated by complementing the dataset with active t-LiDAR measurements. The multispectral analysis of distinct layers corresponds well with the experience-based conventional trench logging. Based on this, a 3D-interpretation of GPR data collected on the vertical trench wall was possible. This allows layer thicknesses and subsurface geometries to be estimated.
Subsurface coseismic features like displaced strata or colluvial wedges, which primarily occur wi... more Subsurface coseismic features like displaced strata or colluvial wedges, which primarily occur within the unconsolidated sediments of the hanging-wall, form important archives as they are used to identify paleoearthquakes and estimate the seismic hazard potential for active fault zones. Traditionally, trenching investigations form a major element of paleoseismic research. For decades now this has comprised manual logging and photomosaic methods. Furthermore, the outcome from using these established techniques is highly dependent on the experience of the trench logger to define mappable units; discrete deposits that are composed of similar lithology need to be distinguished from adjacent units. In order to prove whether the aforementioned trench logging methods used to map coseismic features in a paleoseismic trench walls can be enhanced with objective methods, we combined routine logging with vertical ground-penetrating radar (GPR) measurements and t-LiDAR scans at the Sfaka fault (...
Shallow earthquakes (< 15 km) of a magnitude M > 6.0 on active normal faults leave footprin... more Shallow earthquakes (< 15 km) of a magnitude M > 6.0 on active normal faults leave footprints along the rupture zone; scarps are formed in the landscape which displace the surface, and in the shallow subsurface colluvial wedges (a consequence of degradation of the scarp) and displaced strata commonly occur. These subsurface coseismic features, which primarily occur within the unconsolidated sediments of the hanging-wall (downthrown block), form important archives as they are used to identify paleoearthquakes and estimate the seismic hazard potential for active fault zones. Traditionally, trenching investigations within the fault zone form a major element of paleoseismic research. For decades now this has comprised manual logging and photomosaic methods. Furthermore, the outcome from using these established techniques is highly dependent on the experience of the trench logger to define mappable units; discrete deposits that are composed of similar lithology need to be distingui...
Athens and its surroundings have repeatedly been shaken by moderate damaging earthquakes, but str... more Athens and its surroundings have repeatedly been shaken by moderate damaging earthquakes, but strong local events and severe damage are not proven by instrumental, historical, and archaeological records for the last 2,300 years. Despite this, the surroundings of Athens show clear signs of active faulting. In order to test the hypothesis of Holocene fault activity, we performed field mapping, georadar, morphological analyses and paleoseismological investigations at one of the prominent faults in N Attica, the Milesi Fault. Our data show evidence for recent seismic events and on-going tectonic activity. We can assign a minimum slip rate of 0.3 mm/yr and we are able to identify at least two post-glacial surface-rupturing earthquakes. These results make clear that strong local events in the vicinity of Greece’ capital must be considered in any seismic hazard assessment.
Northern Attica in Greece is characterized by a set of north dipping, subparallel normal faults. ... more Northern Attica in Greece is characterized by a set of north dipping, subparallel normal faults. These faults were considered to have low tectonic activity, based on historical earthquake reports, instrumental seismicity and slip rate estimates. This study presents new data for one of these faults, the Milesi Fault. We run GIS based geomorphological analyses on fault offset distribution, field mapping of postglacial fault scarps and ground penetrating radar profiling to image hangingwall deformation. The first palaeoseismological trenching in this part of Greece allowed obtaining direct data on slip rates and palaeoearthquakes. The trenching revealed downthrown and buried palaeosols, which were dated by radiocarbon. The results of our investigations show that the slip rates are higher than previously thought and that at least four palaeoearthquakes with magnitudes of aroundM6.2 occurred during the last 4000–6000 yr.We calculate an average recurrence interval of 1000–1500 yr and a maximum throw rate of ∼0.4– 0.45 mm a−1. Based on the new geological earthquake data we developed a seismic hazard scenario, which also incorporates geological site effects. Intensities up to IX must be expected for Northern Attica and the southeastern part of Evia. Earthquake environmental effects like liquefaction and mass movements are also likely to occur. This scenario is in contrast to the official Greek seismic hazard zonation that is based on historical records and assigns different hazard zones for municipalities that will experience the same intensity by earthquakes on the Milesi Fault. We show that the seismic hazard is likely underestimated in our study area and emphasize the need to incorporate geological information in such assessments
Two normal faults on the island of Crete and mainland Greece were studied to test an innovative w... more 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 palaeo-seismic 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 mul-tiparametric approaches and shows (i) how a 3-D visualisa-tion 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.
The majority of normal faults on Crete comprise Mesozoic carbonate bedrock fault scarps juxtapose... more The majority of normal faults on Crete comprise Mesozoic carbonate bedrock fault scarps juxtaposed against Quaternary alluvial-colluvial sediments. An outcrop at the west dipping Sfaka fault in the east of the island was studied by combining classical paleoseismic trenching techniques and multispectral approaches. A conventional trench log was compared to results of iso cluster analyses of both a true color photomosaic representing the spectrum of visible light and a near-infrared backscatter signal image from t-LiDAR measurements. The disadvantages of passive data collection (e.g. illumination) were thus negated by complementing the dataset with active t-LiDAR measurements. The multispectral analysis of distinct layers corresponds well with the experience-based conventional trench logging. Based on this, a 3D-interpretation of GPR data collected on the vertical trench wall was possible. This allows layer thicknesses and subsurface geometries to be estimated.
Corinth Gulf is one of the fastest expanding regions worldwide, influenced by several major norma... more Corinth Gulf is one of the fastest expanding regions worldwide, influenced by several major normal faults. We measured the magnetic susceptibility within boreholes, drilled at the footwall and hanging-wall of the Kalamaki fault, a secondary structure that intersects the Corinth Canal. We correlate magnetic susceptibility (MS) measurements with paleoenvironmental and lithological alternations within the boreholes. We have ascribed low MS values to marine highstand deposits and high MS values to lowstand terrestrial deposits. Glacioeustatic sea level changes and tectonic movements have led to a very complicated lithosedimentary pattern, and magnetic susceptibility (MS) measurements can help us interpret the fault's activity.
We present the preliminary results from a multi-method investigation on the Lastros-Sfaka Graben ... more We present the preliminary results from a multi-method investigation on the Lastros-Sfaka Graben located in the Ierapetra Fault Zone in eastern Crete. We scanned c. 1.2 km of the Lastros Fault with t-LiDAR and identified areas for throw rate calculations at locations with no external influences (anthropogenic or erosional). Preliminary maximum throw rates are 0.7 mm/yr, which is significantly less than stated in the literature. Cemented colluvium is located on the Lastros Fault, forming hanging-wall talus lobes and sheets of varying thickness attached to the fault plane. The cement is formed of calcite and further laboratory analyses are underway to determine its formation processes. GPR has been undertaken at the Lastros Fault and cemented colluvium is also present within the hanging-wall subsurface. Road cut (trenching) investigations on the Sfaka Fault identified fill material most likely deposited soon after the last paleoearthquake(s) that occurred on the fault; 14 C dating is ...
Corinth Gulf is one of the fastest expanding regions worldwide, influenced by several major norma... more Corinth Gulf is one of the fastest expanding regions worldwide, influenced by several major normal faults. We measured the magnetic susceptibility within boreholes, drilled at the footwall and hanging-wall of the Kalamaki fault, a secondary structure that intersects the Corinth Canal. We correlate magnetic susceptibility (MS) measurements with paleoenvironmental and lithological alternations within the boreholes. We have ascribed low MS values to marine highstand deposits and high MS values to lowstand terrestrial deposits. Glacioeustatic sea level changes and tectonic movements have led to a very complicated lithosedimentary pattern, and magnetic susceptibility (MS) measurements can help us interpret the fault's activity.
We present the preliminary results from a multi-method investigation on the Lastros-Sfaka Graben ... more We present the preliminary results from a multi-method investigation on the Lastros-Sfaka Graben located in the Ierapetra Fault Zone in eastern Crete. We scanned c. 1.2 km of the Lastros Fault with t-LiDAR and identified areas for throw rate calculations at locations with no external influences (anthropogenic or erosional). Preliminary maximum throw rates are 0.7 mm/yr, which is significantly less than stated in the literature. Cemented colluvium is located on the Lastros Fault, forming hanging-wall talus lobes and sheets of varying thickness attached to the fault plane. The cement is formed of calcite and further laboratory analyses are underway to determine its formation processes. GPR has been undertaken at the Lastros Fault and cemented colluvium is also present within the hanging-wall subsurface. Road cut (trenching) investigations on the Sfaka Fault identified fill material most likely deposited soon after the last paleoearthquake(s) that occurred on the fault; 14 C dating is ...
The majority of normal faults on Crete comprise Mesozoic carbonate bedrock fault scarps juxtapose... more The majority of normal faults on Crete comprise Mesozoic carbonate bedrock fault scarps juxtaposed against Quaternary alluvial-colluvial sediments. An outcrop at the west dipping Sfaka fault in the east of the island was studied by combining classical paleoseismic trenching techniques and multispectral approaches. A conventional trench log was compared to results of iso cluster analyses of both a true color photomosaic representing the spectrum of visible light and a near-infrared backscatter signal image from t-LiDAR measurements. The disadvantages of passive data collection (e.g. illumination) were thus negated by complementing the dataset with active t-LiDAR measurements. The multispectral analysis of distinct layers corresponds well with the experience-based conventional trench logging. Based on this, a 3D-interpretation of GPR data collected on the vertical trench wall was possible. This allows layer thicknesses and subsurface geometries to be estimated.
Subsurface coseismic features like displaced strata or colluvial wedges, which primarily occur wi... more Subsurface coseismic features like displaced strata or colluvial wedges, which primarily occur within the unconsolidated sediments of the hanging-wall, form important archives as they are used to identify paleoearthquakes and estimate the seismic hazard potential for active fault zones. Traditionally, trenching investigations form a major element of paleoseismic research. For decades now this has comprised manual logging and photomosaic methods. Furthermore, the outcome from using these established techniques is highly dependent on the experience of the trench logger to define mappable units; discrete deposits that are composed of similar lithology need to be distinguished from adjacent units. In order to prove whether the aforementioned trench logging methods used to map coseismic features in a paleoseismic trench walls can be enhanced with objective methods, we combined routine logging with vertical ground-penetrating radar (GPR) measurements and t-LiDAR scans at the Sfaka fault (...
Shallow earthquakes (< 15 km) of a magnitude M > 6.0 on active normal faults leave footprin... more Shallow earthquakes (< 15 km) of a magnitude M > 6.0 on active normal faults leave footprints along the rupture zone; scarps are formed in the landscape which displace the surface, and in the shallow subsurface colluvial wedges (a consequence of degradation of the scarp) and displaced strata commonly occur. These subsurface coseismic features, which primarily occur within the unconsolidated sediments of the hanging-wall (downthrown block), form important archives as they are used to identify paleoearthquakes and estimate the seismic hazard potential for active fault zones. Traditionally, trenching investigations within the fault zone form a major element of paleoseismic research. For decades now this has comprised manual logging and photomosaic methods. Furthermore, the outcome from using these established techniques is highly dependent on the experience of the trench logger to define mappable units; discrete deposits that are composed of similar lithology need to be distingui...
Athens and its surroundings have repeatedly been shaken by moderate damaging earthquakes, but str... more Athens and its surroundings have repeatedly been shaken by moderate damaging earthquakes, but strong local events and severe damage are not proven by instrumental, historical, and archaeological records for the last 2,300 years. Despite this, the surroundings of Athens show clear signs of active faulting. In order to test the hypothesis of Holocene fault activity, we performed field mapping, georadar, morphological analyses and paleoseismological investigations at one of the prominent faults in N Attica, the Milesi Fault. Our data show evidence for recent seismic events and on-going tectonic activity. We can assign a minimum slip rate of 0.3 mm/yr and we are able to identify at least two post-glacial surface-rupturing earthquakes. These results make clear that strong local events in the vicinity of Greece’ capital must be considered in any seismic hazard assessment.
Northern Attica in Greece is characterized by a set of north dipping, subparallel normal faults. ... more Northern Attica in Greece is characterized by a set of north dipping, subparallel normal faults. These faults were considered to have low tectonic activity, based on historical earthquake reports, instrumental seismicity and slip rate estimates. This study presents new data for one of these faults, the Milesi Fault. We run GIS based geomorphological analyses on fault offset distribution, field mapping of postglacial fault scarps and ground penetrating radar profiling to image hangingwall deformation. The first palaeoseismological trenching in this part of Greece allowed obtaining direct data on slip rates and palaeoearthquakes. The trenching revealed downthrown and buried palaeosols, which were dated by radiocarbon. The results of our investigations show that the slip rates are higher than previously thought and that at least four palaeoearthquakes with magnitudes of aroundM6.2 occurred during the last 4000–6000 yr.We calculate an average recurrence interval of 1000–1500 yr and a maximum throw rate of ∼0.4– 0.45 mm a−1. Based on the new geological earthquake data we developed a seismic hazard scenario, which also incorporates geological site effects. Intensities up to IX must be expected for Northern Attica and the southeastern part of Evia. Earthquake environmental effects like liquefaction and mass movements are also likely to occur. This scenario is in contrast to the official Greek seismic hazard zonation that is based on historical records and assigns different hazard zones for municipalities that will experience the same intensity by earthquakes on the Milesi Fault. We show that the seismic hazard is likely underestimated in our study area and emphasize the need to incorporate geological information in such assessments
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