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Dimitrov, Dimitar
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Dimitrov, Dimitar
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- PublicationRestrictedPaleoseismologic investigation of the fault that ruptured in the April 14, 1928, Chirpan earthquake (M 6.8), Southern Bulgaria(2006)
; ; ; ; ; ; ; ; ; ; ;Vanneste, K.; Royal Observatory of Belgium, Brussels, Belgium. ;Radulov, A.; Geological Institute, Bulgarian Academy of Sciences, Sofia, Bulgaria. ;De Martini, P. M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Nikolov, G.; Geological Institute, Bulgarian Academy of Sciences, Sofia, Bulgaria. ;Petermans, T.; Royal Observatory of Belgium, Brussels, Belgium. ;Verbeeck, K.; Royal Observatory of Belgium, Brussels, Belgium. ;Camelbeeck, T.; Royal Observatory of Belgium, Brussels, Belgium. ;Pantosti, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Dimitrov, D.; Institute of Geodesy, Bulgarian Academy of Sciences, Sofia, Bulgaria. ;Shanov, S.; Geological Institute, Bulgarian Academy of Sciences, Sofia, Bulgaria.; ; ; ; ; ; ; ; ; Seventy-five years after the destructive Chirpan earthquake of 14 April 1928, we conducted a paleoseismologic study of the causative fault combining a review of contemporary literature, geomorphology, geophysical prospecting, and trenching. We reidentified the fault scarp in the field, and mapped it over a distance of 12.5 km. Geophysical profiles and boreholes demonstrate that Chirpan scarp is the surface expression of a normal fault that was active throughout the Pleistocene and Holocene. In 2002, we excavated a paleoseismologic trench to study the faulting history. A narrow fault zone separates Plio-Pleistocene alluvial sand in the footwall from Holocene alluvial and colluvial silt in the hanging wall. The 1928 earthquake is recorded by 0.45 m vertical offset of the topsoil, in accordance with contemporary descriptions. We identified three colluvial wedge-like units in the hanging wall sediments next to the fault, evidencing at least three surface-rupturing paleoearthquakes since the Atlantic. Their timing could only be loosely constrained using pollen. The penultimate event had an offset of 0.40– 0.45 m and occurred after circa 2600 calibrated years before present (cal years B.P.). Event 3 displaced a Subboreal semiarid calcic soil 0.55–0.70 m between circa 5750 and 2600 cal years B.P. The fourth event had a minimal offset of 0.50–0.70 m and occurred between circa 8900 cal years B.P. and 4900 B.C., when the region was first settled. We obtain a Holocene fault slip rate of 0.22 ± 0.12 mm/yr and an average recurrence interval of 2350 ± 643 years for earthquakes comparable to or larger than the 1928 event.187 32 - PublicationRestrictedUsing kinematic GNSS data to assess the accuracy and precision of the TanDEM-X DEM resampled at 1 m resolution over the western Corinth Gulf, Greece(2021)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; We assess the accuracy and the precision of the TanDEM-X digital elevation model (DEM) of the western Gulf of Corinth, Greece. We use for that a dense set of accurate ground coordinates obtained by kinematic GNSS observations. Between 2001 and 2019, 148 surveys were made, at 1 s sampling rate, along highways, roads and tracks, with a total traveled distance of ~25,000 km. The data are processed with the on-line Canadian Spatial Reference System precise point positioning software. From the output files, we select 885,252 coordinates from epochs with theoretical uncertainty below 0.1 m in horizontal and 0.2 m in vertical. Using specific calibration surveys we estimate the mean vertical accuracy of the GNSS coordinates at 0.2 m. Resampling the DEM by a factor of ten allows to compare it with the GNSS in pixels of metric size, thus smaller than the width of the roads, even the small trails. The best fit is obtained by shifting the DEM by 0.47 ± 0.03 m upward, 0.10 ± 0.1 m westward, and 0.36 ± 0.1 m southward. Those values are twenty times below the nominal resolution of the DEM. Once the shift is corrected, the root mean square deviation between TanDEM-X DEM and GNSS elevations is 1.125 m. In forest and urban areas, the shift between the DEM and the GNSS increases by ~0.5 m. The metric accuracy of the TanDEM-X DEM paves the way for new applications for long-term deformation monitoring of this area.168 23