Search

The Roman archeological site of Baelo Claudia (Cádiz, south Spain) is located within the Gibraltar Arch, a region with no significant recent or historical seismicity. However, previous studies have emphasized the occurrence of repeated strong archeoseismic damage (intensity >IX MSK) at Baelo Claudia. Identifying the damages in detail and searching for the seismogenic source was the aim of the Baelo Claudia Project - solving the Baelo Claudia earthquake problem. This thesis summarizes the results from the field campaigns in 2005, 2006, 2007, 2008, 2009, and 2010. The text is mainly based on two published and one submitted paper. A multidisciplinary study has been carried out at the archeological site including the detailed mapping of surface deformation and building damage, surface geology and geomorphology, and the collection of structural data. An extensive ground penetrating radar (GPR) survey has been conducted in the ruins for detecting archeoseismologic damages and imaging the subsurface conditions. The obtained data are not conclusive when considered separately, but obvious links between archeoseismic damage, structural and GPR data indicate that the destruction of the city was linked to seismic shaking and that two earthquakes occured within the Roman period. 14C dating results from damaged infrastructure (e.g., the Isis Temple) allow to suppose two devastating events around 40-60AD and 260-290AD. These dates vary from those proposed by earlier studies, which suggested two events in 40-60AD and 350-395AD. The analysis of the pattern and orientation of deformation clearly indicates SW-NE directed compression due to ground shaking. This investigation also focuses on localized landslides and liquefaction processes, which appear to be coeval with the earthquakes, but the poor geotechnical parameters of the clayey substratum were determinant to amplify the observed level of destruction. The application of the present Spanish seismic code (NCSE-02) indicates that intensity VIII MSK (0.24-0.26g) can be reached in this zone for 475 year return periods. Despite the earthquake-related damages and the dating of the events seem to be reliable, the search for the local seismogenic fault(s) was problematic. The damage patterns rather indicate a fault in the vicinity than a far-field event (e.g., the 1755 Lisbon seismic source in the Atlantic). High-resolution shallow geophysics were applied to the local faults mapped in order to get information on their activity; marine seismics in the Bolonia Bay were performed in 2006 for imaging the youngest sediments and active faults offshore. Based on the data, trenches were excavated at the Cabo de Gracia fault a few kilometres W of Baelo Claudia. Off-shore highresolution seismic investigations, structural and paleostress data and trenching studies combined with high-resolution GPR and resistivity point to active faulting along N-S trending normal faults. Hence, N-S directed normal faults in the area are claimed as local candidates for moderate earthquake activity. Paleoseismic evidence for a moderate event around 6000-5000BP has been found along the close-by normal Carrizales fault. This points to three local moderate earthquakes in the last 6000 years, and to return periods on the order of 2000-2500 years. In a third step, the observations have been quantified using the two logic trees for paleoseismology (Atakan et al., 2000) and archeoseismology (Sintubin and Stewart, 2008). The results show that a mere paleoseismological classification of the geological features leads to a paleoseismic quality factor (PQF) of 0.03, which is low compared to other studies. Taking into account the additional information from archeoseismological work (archeoseismological quality factor [AQF] is 0.5), it becomes clear that the Baelo Claudia study site provides an opportunity for detailed earthquake investigations. Therefore, it has a high potential for reliable seismic hazard analyses. A complementary application of both logic trees is recommended in future studies if sufficient data are available. The study illustrates that a multi-disciplinary approach in archeo- and paleoseismology is required for reliable data. It is shown that the southernmost part of the Iberian peninsula is characterized by a significant seismic hazard and that the Roman ruins of Baelo Claudia have preserved the earthquake information, even though it was not easy to gather.

A significant amount of the ongoing shortening between the Eurasian and Arabian plates is accommodated within the Zagros Fold‐Thrust Belt. However, the spatial and temporal distribution of active shortening within the belt, especially in its NW part, is not yet well constrained. We determined depositional ages of uplifted river terraces crossing the belt along the Greater Zab River using luminescence dating. Kinematic modeling of the fault‐related fold belt was then used to calculate long‐term slip rates during the Late Pleistocene to Holocene. Our results provide new insight into the rates of active faulting and folding in the area. The Zagros Mountain Front Fault accommodates about 1.46 ± 0.60 mm a−1 of slip, while a more external basement fault further to the SW accommodates less than 0.41 ± 0.16 mm a−1. Horizontal slip rates related to detachment folding of two anticlines within the Zagros Foothills are 0.40 ± 0.10 and 1.24 ± 0.36 mm a−1. Basement thrusting and thickening of the crust are restricted to the NE part of the Zagros belt. This is also reflected in the regional topography and in the distribution of uplifted terraces. In the southwestern part, the deformation is limited mainly to folding and thrusting of the sedimentary cover above a Triassic basal detachment. In the NE, deformation is associated with slip on basement thrusts. Our study sheds light on the distribution of shortening in the Zagros Mountains and helps to understand the regional tectonic system. Our results may be the foundation for a better seismic hazard assessment of the entire area., Plain Language Summary: In active mountain belts, river terraces found above the present‐day river level can be indicative of differences in uplift rates due to the thickening, faulting, and folding processes in the Earth's crust. These processes, driven by the motion of tectonic plates, are responsible for the formation of mountain belts. Here, we took sediment samples from uplifted river terraces along the Greater Zab River that crosses the Zagros Mountains in the Kurdistan Region of Iraq. We determined their deposition age using luminescence dating. From their age and elevation, we calculated uplift rates. We built a geometrical model of the fault zones in the area and determined how fast the slip occurs on these faults based on the uplift rates. Our results indicate that there were less than two millimeter per year of slip on these faults on average during the last 60 thousand years. This motion is a result of the convergence between the Arabian and Eurasian plates. With studies like this we can measure how fast fault blocks move, even if they were not associated with large earthquakes in the recent past. This approach helps to better assess the potential earthquake hazard in the area under investigation., Key Points: We estimated fault slip rates in the NW Zagros Mountains by luminescence dating of river terraces and structural modeling. There is c. 1.46 mm a−1 slip on the Mountain Front Fault and c. 1.64 mm a−1 slip from detachment folding in the NE part of the Foothill Zone. Crustal thickening and basement thrusting occur in the NE parts of the Foothill Zone and only cover deformation occur in the SW parts., German Academic Exchange Service (DAAD) http://dx.doi.org/10.13039/501100001655, German Research Foundation (DFG) http://dx.doi.org/10.13039/501100001659