Paleoseismic Phenomena in Karst Terrains in Bulgaria and Morocco

Abstract

V zadnjih letih narašča zanimanje za beleženje in raziskovanje učinkov paleoseizmičnih dogodkov na kraškem površju in v podzemlju. Kras je lahko zanesljiva referenčna točka za razumevanje potencialne seizmičnosti na področjih, kjer opazovalni inštrumenti kažejo nizko oziroma zmerno seizmičnost. V Bolgariji in Maroku zavzema kras velike površine. Spremembe na kraškem površju in v podzemlju navadno povzročijo katastrofalni trenutni dogodki ali pa ponavljajoča se premikanja zaradi potresov. Katastrofalni potresni dogodki so spremenili medsebojno povezane kraške ekosisteme in so bili vzrok za pomlajevanje, reaktiviranje ali prekinitev kraških procesov. Naravni površinski ali podzemeljski relief sta bila deloma ali v celoti uničena; nastal je nov tip reliefa; geološko okolje je bilo spremenjeno; nastale so spremembe v količini odtoka in v smeri površinskega in podzemeljskega odtekanja kraške vode; nastali so gravitacijski tipi močvirij; kraške jame, lokalni tektonski jarki, prihajalo je do podorov in zemeljskih plazov in ozemlje je bilo podvrženo grezanju in uničenju; spremenjeno je bilo ekološko ravnotežje urbaniziranih pokrajin. V pričujočem delu je govora o različnih paleoseizmičnih pojavih na krasu v Bolgariji in v Maroku. Na podlagi preučevanja tektonskih premikov so dana priporočila za varstvo teh ozemelj.

During the recent years there has been a growing interest in recording and investigating the effects of paleoseismic events in surface and underground karst in almost all countries. Karst represents a reliable reference marker for understanding the potential seismicity in regions with instrumentally established low to moderate seismicity. The karst terrains in Bulgaria and Morocco occupy considerable areas. The disturbances in surface and underground karst had usually been provoked by catastrophic one-act events or by repeatedly activated movements by earthquakes. The catastrophic seismic events had disturbed the naturally interrelated karst ecosystems and were the reason for rejuvenation, reactivation or attenuation of karst processes. The natural surface and underground relief had been partially or entirely destroyed; a new type of relief had been formed; the geological environment had been disturbed; changes occurred in the flowrate and direction of surface and underground karst water; wetlands of the gravitation type had been formed; natural caves, local grabens, rock-falls and landslides collapsed partially or entirely and terrains were subjected to subsidence and destruction; the ecological balance in urbanized territories had been disturbed. The present work considers the different types of paleoseismic phenomena in the karst terrains in Bulgaria and Morocco. Recommendations are given for the protection of these areas.