Earthquake impact and interaction in delta-lobe formation and channel migration

Sefidrud delta is the largest delta in the South Caspian basin and as other rivers and deltas is a human populations and productive ecosystem services in the north of Iran. Experimental investigations show several delta lobes and migration through the time. Many processes control the river avulsion and delta-lobe formation and their migrations, that may impact the human life. Climate changes, base-level and sea-level changes and tectonic activities are the main controlling factors of the deltas changes. This study tries to investigate the latest delta lobe and channel migration of the Sefidrud delta based on satellite images and field investigations from ۱۹۷۰ to the present. Satellite image analysis show that the Sefidrud delta lobe has been started to migration from ۱۹۹۰. The first clue of the migration recorded by occurrence of the new narrow channel on the east of the delta in satellite images. Next year, there were two main channels, the previous channel and new one and a part of the sediment load deposited at the new channel mouth bar. On the ۱۹۹۲, the eastern channel acted as the main channel and new delta lobe has started to formation in new location. Flooding and deposition of the floodplain and crevasse splays are the other observable data. Channel and delta-lobe migrations are synchronous with the earthquake of ۲۰ January ۱۹۹۰ of the Rudbār (Manjil) in Alborz Mountain region of Iran as the second largest strike-slip earthquake to have occurred in an intracontinental setting in the past decade. Based on literature, the earthquake was associated with faulting and folding, and with maximum ۶۰ cm horizontal and ۹۵ cm vertical surface displacement in more than ۸۰ km NW–SE trending left-lateral strike-slip faulting. There were many small to large landslides along Qezel Ozan and Sefidrud rivers. Lake of the other controlling processes such as base/sea-level changes, sedimentological structures and facies changes can be conclude that the related Rudbar earthquake faulting and folding were the main factor for increasing of the sediment supply and Sefidrud delta lobe and channel migrations and flooding during ۱۹۹۰ to ۱۹۹۴ and formation of the current delta lobe.

کلیدواژه ها:

Delta ، Tectonic activity ، Earthquake ، Sefidrud ، Rudbar