Christoph Grützner

Surface and subsurface palaeoseismic records at the ancient Roman city of Baelo Claudia and the Bolonia Bay area, Cádiz (south Spain)

Abstract The Roman archaeological 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 archaeoseismic damage (intensity≥IX MSK) at Baelo Claudia tentatively bracketed in this study around ad 40–60 and ad 260–290. A multidisciplinary study has been carried out including the detailed mapping of surface deformation and building damage, surface geology and geomorphology, collection of structural data, and an extensive ground penetrating radar (GPR) survey. The obtained data are not conclusive when considered separately, but evident links between archaeoseismic damage, structural and GPR data indicate that the destruction of the city was linked to seismic shaking. The analysis of the pattern and orientation of deformation clearly indicates SW–NE directed compression due to ground shaking. This analysis 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 (0.24–0.26 g) can be reached in this zone for 500 year return periods.

The impact of the 1945 Makran tsunami along the coastlines of the Arabian Sea (Northern Indian Ocean) - a review

The Makran Subduction Zone marks the plate boundary between the Arabian and Eurasian plate within the northern Arabian Sea. The only instrumentally recorded earthquake (MW 8.1) that triggered a tsunami along this subduction zone occurred on 27 November, 1945. We summarise and review individual observations of both: earthquake and tsunami. Published scientific reports, newspaper articles as well as eye- witness accounts are used. The information gathered reveals the impact along the shorelines of the Arabian Sea. It is evident that the most severe impact was encountered along the Pakistani shoreline in close proxim- ity to the epicentre of the earthquake. Additionally, the low lying Indus river delta was severely affected. The most distant record of the tsunami is located on the Seychelles Islands; 3,400 km from the epicentre. The tsunami was observed along the eastern shoreline of Oman. Several eyewitnesses report that the sea rose unexpectedly. A storm event is excluded, as such would have been recognised beforehand. The damages reported for the Omani coastline are only minor. However, locally the coastline is decorated by boulder and block deposits. These are interpreted as indicative for palaeo-tsunami with higher run-ups. The total number of casualties along the entire area of impact is estimated in the order of a couple of hundreds. Reports of several thousand casualties are exaggerated and derive from early estimations that were not confirmed.

Active basins and neotectonics: morphotectonics of the Lake Ohrid Basin (FYROM and Albania) [Aktive Becken und Neotektonik: die Morphotektonik des Ohridbeckens (FYROM und Albanien).]

The Lake Ohrid Basin in FYROM (Former Yugoslav Republic of Macedonia) and Albania meets all criteria of an active, seismic landscape: linear step-like fault scarps in the landscape and under water within the lake. Post-glacial (or Late Pleistocene) bedrock fault scarps at Lake Ohrid are long-lived expressions of repeated surface faulting in tectonically active regions, where erosion cannot outpace the fault slip. Other morphotectonic features are wind gaps, wineglass-shaped valleys and triangular facets, which are well preserved. Generally, the faults and fault scarps are getting younger towards the basin centre, as depicted on seismic and hydroacoustic profiles. Additionally, mass movement bodies within the lake and also onshore (rockfalls, landslides, sub-aquatic slides, homogenites, turbidites) are likely to have been seismically triggered. These morphotectonic observations are in line with focal mechanisms of earthquakes in the greater Lake Ohrid area. We investigated the neotectonic history and tectonic geomorphology of the Lake Ohrid Basin by means of an integrated multidisciplinary approach, using tectonic geomorphology and a variety of geophysical and remote sensing methods.

An Indian Ocean tsunami triggered remotely by an onshore earthquake in Balochistan, Pakistan

This paper describes and documents instrumentally recorded tsunami waves that are interpreted as secondary effects of a 7.7 magnitude earthquake in southern Pakistan on 24 September 2013. The tsunami waves were almost unnoticed because the wave heights were low and the tsunami occurred at low tide. The historical record of tsunami events within the Arabian Sea (northern Indian Ocean) is fragmentary. Large tsunamigenic earthquakes are known to be generated in the Makran subduction zone, the area that forms the boundary of the Arabian and Eurasian plates. Submarine sliding is reported along the Owen Fracture Zone, which marks the boundary between the Arabian and Indian plates. Hence, the tsunami hazard potential within the Arabian Sea is enigmatic. Our analysis is based on sea-level oscillations recorded at various tide-gauge stations along the coastlines of Oman, Pakistan, and Iran, as well as eyewitness accounts of the event in Oman. Our results indicate that the waves were in the range of 1 m or less in height. They were first recorded along the eastern coast of Oman, and propagated toward the west. We suggest that the waves must have been triggered by a submarine slide on the Makran margin. Cascading effects resulting in large submarine slope failures within the Arabian Sea are more frequent than postulated. The hazard potential is underestimated, as such secondary effects of distant ruptures onshore were previously not taken into account.

Quaternary coastline evolution of Lake Ohrid (Macedonia/Albania)

Lake Ohrid (between FYR of Macedonia and Albania), situated in an active tectonic region of the Balkanides, is characterized by N — S trending active faults. To reconstruct the Holocene shoreline evolution we investigated the coastline using sediment cores and geophysical methods to image sedimentary and tectonic structures. We revealed areas of differing sedimentation regimes. The plains north and south of the lake are dominated by clastic input related to climate variations and uplift/erosion, whereas the steep western and eastern margins are controlled by recent tectonics. Furthermore, no evidence for a much higher lake-level during the Holocene was found in the plains north and south of the lake, except rare temporary floodings. This is supported by mappings of the limestone cliffs around Lake Ohrid, which yielded no evidence for abrasional platforms or notches as indicators for past highstands.

Identifying sedimentary structures and spatial distribution of tsunami deposits with GPR - examples from Spain and Greece

Shallow drilling in coastal areas like southern Spain and different parts of Greece (Corinth region and Argolis Gulf) proved evidence for tsunamis. Sedimentary analyses were conducted to identify tsunamigenic deposits, but did not reveal sedimentary structures or spatial distribution of tsunamites in a regional scale. Since drilling is time-intensive and expensive (depending on extend), this method can by far not cover an entire coastal area. On the other hand, distribution and preservation of tsunamigenic deposits seems to be highly variable. We used ground penetrating radar (GPR) in combination with electrical resistivity tomography (ERT) measurements and sedimentological research methods for tsunamite detection in Greece and Spain. The combination of these three methods enables an improved interpretation of the results and 3D visualization, which give clues for tsunamite distribution and sediment architecture. GPR data indicate unconformable thicknesses of tsunamigenic beddings, channel-like structures (back wash deposits), in some extent chaotic erosion basement, as well as abrasion-scours in various places, and boulder accumulation inside the deposits. In the future, GPR and other shallow geophysical methods will be used to detect run-up distances and typical sediment structures.

Improving archaeological site analysis: a rampart in the middle Orkhon Valley investigated with combined geoscience techniques

The Orkhon Valley in the Central Mongolia was included in the World Heritage list in 2004. It hosts multiple archaeological sites from Palaeolithic to recent times, which can contribute to the reconstruction of settlement history in this part of the Eurasian Steppe landscape. Almost 100 archaeological sites from prehistoric and historic times including ramparts and khirigsuurs were investigated in five field campaigns from 2008 to 2010 in the middle and upper Orkhon Valley. One site, MOR-2 (Dorvolzhin), proved especially difficult to date due to the lack of sufficient archaeological surface finds, and its role within a manifold of walled enclosures from different times in the study area remained unclear. Therefore, different techniques of archaeology, geophysics and geoarchaeology were combined at MOR-2 in order to determine a comprehensive picture about its timing, archaeological meaning, and environmental history. Information on topographical setting and morphometry of the rampart was gathered by an octocopter equipped with a high-resolution range finder camera. We achieved a high-resolution DEM that allowed us to map the rampart in detail and this served as a base map for all other investigations. SQUID magnetometry, ground-penetrating radar, and electric resistivity measurements (capacitive coupled geoelectrics) were subsequently used to detect archaeological remains and to characterize the sediment distribution of the inner part of the enclosure and the ramparts themselves. The data show that the construction of the walls is similar to well-known Uighur neighbouring sites. Man-made sub-surface structures or bigger finds could not be detected. Sediment cores were drilled in a nearby meander, covering 3000 years BP. The analysis of the strata in terms of elemental composition (P, N, Mn, Fe, etc) revealed an increase of organic content in Medieval times, whereas the allochthonous filling of the back water must have started around the beginning of the 6th century AD. Using geophysical, archaeological and geological observations, we assume a dating in the Turk/Uighur period (6th–9th century AD) and a re-use under Mongolian reign (12th–17th century AD). This would mean that this site is the furthermost walled structure in the peri-urban area of Khar Balgas. However, the specific usage of this walled enclosure remains unclear and needs further analysis.

Mapping Buried Karst Features with Capacitive-Coupled Resistivity System (CCR) and Ground Penetrating Radar (GPR)

Surface near karst features in catchment areas of drinking water abstraction points are possible hotspots for groundwater contamination. In karst areas with absent or patchy cover sediments, karst features can be mapped with traditional techniques or by image processing of satellite images or aerial photographs. Karst features which are buried below thin soil or sediment cover may not necessarily be identified with these techniques. In a karst area in western Germany, geophysical surveys have been tested to identify karst features below a relatively thin soil cover, which have been refilled for agricultural purposes. Resistivity measurements (OhmMapper) and ground penetrating radar (GPR) have been applied on a site, where the presence of karst features (dolines) is historically proven. The results of the OhmMapper survey show distinct distribution of resistivity for those transects where high resistivity is interpreted as limestone and low resistivity is interpreted as soil, sediments and filled dolines. The results of the GPR survey are weak, and the structures of the filled dolines are not clearly represented by the GPR logs. This is probably due to the wet hydrological conditions during the measurement campaign. Capacitive-coupled resistivity measurement (CCR) is a suitable technique to identify surface near buried karst features. The CCR measurement can therefore be a useful supplement during the delineation of groundwater protection areas in karst areas where buried karst features are supposed.

Active tectonics around Almaty and along the Zailisky Alatau rangefront

This is the author accepted manuscript. The final version is available from Wiley via http://onlinelibrary.wiley.com/doi/10.1002/2017TC004657/abstract

Holocene tsunamigenic sediments and tsunami modelling in the Thermaikos Gulf area (northern Greece)

Shallow drill cores in fl at and southerly exposed coastal areas around the Th ermaikos Gulf (Th essaloniki, northern Greece) provided evidence for past high energy sedimentary events, which are interpreted as tsunamites. A tsunamigenic source is located along the western tip of the North Anatolian Fault Zone (NAFZ) in the North Aegean Basin, where water depths ranging between 1.200 and 1.650 m are suffi ciently deep to generate tsunamis. However, the event layers up to now cannot be assigned to individual seismic or landslide sources, but the potential of a tsunami threat in the Th ermaikos Gulf area can now be tested, following both sedimentological and modelling processes. Such potential threat regarding the Th ermaikos Gulf has only recently been notifi ed, but never tested and studied in depth. As a result, several Holocene coarse clastic marine layers have been found intercalated in clayey or gypsiferous lagoonal deposits. Th ese layers have erosive bases, show fi ning-up and thinning-up sequences, and include shell debris, foraminifera and rip-up clasts of lagoonal sediments. A widely observed signifi cant feature of these layers involves mud-coated beach clasts, clasts that rework the high-plasticity clays of lagoons. Such features that indicate highly disturbed sedimentological processes (hyperpycnal fl ows) are rarely described elsewhere. Multiple intercalations of these layers with all the mentioned indicative features downhole are interpreted as paleotsunami deposits from tsunamis generated by earthquakes or earthquake-triggered submarine landslides in the Th ermaikos Gulf. Modelling of the tsunami potential of the basin-bounding fault southwards of the Th ermaikos Gulf provides an example for possible tsunami generation at only one segment of NAFZ along an approx. 55 km normal fault at the southern fault-bound margin of the North Aegean Basin.