Bar-Matthews, Miryam

Two underground cavities in the Northern Calabria region, the Romito and the San Paolo caves, have been selected for speleoseismic analysis in order to provide a timeframe for paleoearthquakes which have shocked the cave sites and the surrounding area. The caves are positioned in a seismogenically active region, which has been struck by medium to large earthquakes in historical and pre-historic times. Moreover, frequent instrumentally measured small to moderate seismicity occurs in the area (M 5.6). We document damaged carbonate cave deposits, including collapsed and broken stalactites, in-situ severed stalagmites and stalactites, and collapsed bedrock ceilings. Samples were sawed in order to expose breakages and contacts within the laminae. Sixteen laminae, eight pairs of pre and post event laminae, were drilled for dating by the UraniumeThorium disequilibrium technique. Three discrete events were defined by six of the speleoseismites to (I) 7.4e2.9 ka, (II) 9.7e8.2 ka, and (III) 28.4e27.4 ka. Two additional speleoseismites gave wide age brackets, but are confined to 65.7e18.6 ka, which overlaps with event III, but might represent additional events. The present speleoseismic work depicts a scenario of a minimum of three well-constrained strong shaking events in a time span of the past ~28 ky, yielding a maximum recurrence interval of ~9 ky. In 2012 the area was shaken by a Mw5.2 earthquake that apparently did not produced damage within the study cavities, suggesting that this size is a lower magnitude limit for producing permanent effects in the caves deposits. The speleoseismites we studied collected must have been generated by larger magnitude events, and/or with different epicenter locations. This study adds medium or large earthquake events, previously lacking, to the historic and instrumental record. This may contribute to reduction of gaps in the earthquake record and consequently a more reliable recurrence interval estimate for damaging earthquakes in the region.

Soreq (Israel) and Corchia (central Italy) Caves are located 2500 km far apart along the Mediterranean winterstormtrack and are ideally suited for investigating past variations of winter rainfall in the Mediterranean region. Analyses of speleothem δ18O records from both caves for the period between ca. 7 to 4 ka BP show some striking similarities for the ca. 6 and 4 ka interval, but lack agreement between ca. 7 to 6 ka BP. Two prominent isotopic excursions, argued to reflect relatively drier conditions, are centred at ca. 5.6 and ca. 5.2 ka. The 5.2 ka event lasts less than a century, whereas the 5.6 ka event extends fromca. 5.7 to 5.4 ka. A period of progressive drying is also apparent fromca. 5 to 4 ka. Another prominent event, reflecting wetter conditions, is recorded in both records at ca. 5.8 ka and seems to last several decades. The 5.6 and 5.2 ka events occurred within a period of higher deposition of haematite-stained grains in cores of the sub-polar North Atlantic, and correlationwith the wind strength proxy record fromHólmsá loess profile in Iceland suggests that rainfall reductionwas related to a reduced vapour advection from Atlantic towards the Mediterranean connected to northward shift in the Westerlies. A comparisonwith Alpine records, including the Spannagel Cave isotope record, suggests that dry events recorded at Soreq and Corchia caves may correspond to wetter (lake high stands) and cooler (glacier expansion) conditions in the Alpine region, indicating complex regional climate re-organization.