Spätquartäre Erdbebengeschiche von Festgesteins-Abschiebungen ermittelt durch 36Cl, LiDAR und REE Messungen, sowie Schlussfolgerungen zur methodischen Anwendung, zu den Bewegungsraten der Störungen und zum seismischen Zyklus
Zusammenfassung der Projektergebnisse
Bedrock normal faults are frequent geomorphic features, particularly in the Mediterranean area. They occur as well-preserved limestone fault scarps composed of several meters high fault planes which extend over several kilometers length (typically 5-20 km). These fault scarps result from stepwise exhumation during cumulative displacements of individual earthquakes, as shown during the 2016 Apennine and the 1981 Alkyonides earthquake sequences. This study used the naturally exposed bedrock fault planes to reveal the seismic history of the faults. Therefore, we developed an innovative approach of different mapping techniques (visual, photogrammetry, t-LiDAR) to determine the exact location of different exhumation stages, followed by selected analysis of 36Cl samples to date paleoearthquake events. We selected three bedrock normal fault scarps in Greece, i.e. the Pisia fault in the Gulf of Corinth, the Lastros fault in eastern Crete and the Spili fault in central Crete. All observations were restricted to study sites with negligible non-tectonic processes. Hence, locations with anthropogenic, erosional, depositional or sliding influences were avoided. This accounts also for numerous sites with cemented colluvium that is attached to the fault planes, since that it is not suitable to obtain paleoseismic information according to our analysis. The interdisciplinary mapping of different weathering-related surface properties along the exposed fault planes revealed distinct stripes that are related to past exhumation events. The stripes were detected by color changes, lichen colonization and different karst features (pitting, solution flute terminations, roughness differences). For instance, at the base of the 25-km-long Pisia fault, a clear stripe of contrasting color occurs, whose height is in accordance with the reported exhumation of ~0.6-1.5 m during the 1981 Alkyonides earthquake sequence. Above this stripe, we observed five to seven additional stripes of 25-100 cm height. Similar horizontal stripes were revealed along the fault planes of the ~11-km-long Lastros fault and the ~18-kmlong central Spili fault, indicating 20-30 cm and 35-45 cm coseismic offset, respectively. Based on these offsets, the paleoearthquake magnitudes on these faults reached M 6.2-6.7. The timing of individual earthquakes was successfully constrained using statistical modeling of cosmogenic 36Cl concentrations. At the three faults, earthquake ages could be determined, which reach back up to ~7.0 kyr. The age uncertainties of the individual events are ~±0.7 kyr, which is in the same range as age uncertainties in traditional paleoseismic trenches. Thanks to our interlaboratory calibration study, it is ensured that the 36Cl concentrations are comparable to results derived from other 36Cl laboratories. This study demonstrated that the fault scarps are not necessarily of postglacial age as suggested in several previous publications. This means that slip rates cannot be determined precisely without age determinations. This study showed that the amount of required 36Cl samples can be significantly reduced compared to previous practice. Simultaneously, the accuracy of the reconstructed earthquake history is improved based on the independent detection of the location of paleoearthquake horizons. The three studied normal faults indicate significant variabilities of their long-term slip rates ranging between 0.2 to 2.0 mm/yr during the last ~17 kyr. This reveals major aspects of the fault mechanics and contributes to the understanding of the dynamic properties in similar geologic settings. These slip rate variabilities together with the uncharacteristic earthquake recurrences highlight the complexity of the process and of a reliable evaluation of seismic hazards. In summary, this study showed for the first time that the chosen investigations on bedrock fault planes are a valuable option to reconstruct the complete history of strong Holocene earthquakes.
Projektbezogene Publikationen (Auswahl)
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(2015): The slip history of the Pisia fault, Gulf of Corinth, based on bedrock fault scarp analyses. 6th International INQUA Meeting on Paleoseismology, Active Tectonics and Archeoseismology, Fucino, Italy, 19.-24. April 2015, 289-292
Mechernich, S., Mason, J., Papanikolaou, I., Binnie, S., Reicherter, K. & Dunai, T.
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(2016): Fault structure and deformation rates at the Lastros-Sfaka Graben, Crete. Tectonophysics 683, 216-232
Mason, J., Schneiderwind, S., Pallikarakis, A., Wiatr, T., Mechernich, S., Papanikoloau, I. & Reicherter, K.
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(2016): Slip history of the Pisia fault segment (Gulf of Corinth) based on bedrock fault scarp analyses. TSK16, Bonn, Germany, 1.-6.03.2016
Mechernich, S., Mason, J., Reicherter, K., Papanikolaou, I., & Dunai, T.
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(2017): A multi-method investigation at the Lastros-Sfaka Graben, Crete. Proceedings of the 14th International Congress of the Geological Society of Greece, Thessaloniki, Greece, 25.-27. May 2016. In: Bulletin of the Geological Society of Greece 50, 85-93
Mason, J., Schneiderwind, S., Pallikarakis, A., Wiatr, T., Mechernich, S., Papanikoloau, I. & Reicherter, K.
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(2017): Hanging-wall colluvial cementation along active normal faults. Quaternary Research, 88(01), 39-59
Mason, Jack; Schneiderwind, Sascha; Pallikarakis, Aggelos; Mechernich, Silke; Papanikolaou, Ioannis & Reicherter, Klaus
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(2018): Advances in cosmogenic chlorine-36 dating applications. GeoBonn, 02.-06. Sep. 2018
Mechernich, S., Gromig, R., Goral, T., Binnie, S.A. & Dunai, T.
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(2018): Paleoseismology using bedrock fault planes. Geophysical Research Abstracts, Vol. 20, EGU2018-18973
Mechernich, S., Schneiderwind, S., Mason, J., Biermanns, P., Schmitz, B., Papanikolaou, I. & Reicherter, K.
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(2018): Postglacial slip rate variability of the Lastros normal fault (eastern Crete, Greece). 9th International INQUA Meeting on Paleoseismology, Active Tectonics and Archeoseismology, Possidi, Greece, 27.-29. June 2018, 168-171
Mechernich, S., Dahms, H., Reicherter, K. & Papanikolaou, I.
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(2018): The seismic history of the Pisia fault (eastern Corinth rift, Greece) from fault plane weathering features and cosmogenic 36Cl dating. Journal of Geophysical Research – Solid Earth, 123, 4266-4284
Mechernich, S., Schneiderwind, S., Mason, J., Papanikolaou, I., Deliginnakis, G., Pallikarakis, A., Binnie, S., Dunai, T. & Reicherter, K.
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(2019) Carbonate and silicate intercomparison materials for cosmogenic 36Cl measurements. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 455 250–259
Mechernich, Silke; Dunai, Tibor J.; Binnie, Steven A.; Goral, Tomasz; Heinze, Stefan; Dewald, Alfred; Schimmelpfennig, Irene; Keddadouche, Karim; Aumaître, Georges; Bourlès, Didier; Marrero, Shasta; Wilcken, Klaus; Simon, Krista; Fink, David; Phillips, Fred M.; Caffee, Marc W.; Gregory, Laura C.; Phillips, Richard; Freeman, Stewart P.H.T.; ... & Vockenhuber, Christof
