Active faulting, earthquakes, and geomorphology of the Main Kopeh Dagh fault, Turkmenistan

We present initial results from a study of the active faults defining the margins of the South Caspian Basin,which is itself an enigmatic deep-water basin that appears to move relative to adjacent parts of Iran andEurasia. We report on recent field-based estimates of the slip rates of the Main Kopeh Dagh (MKDF) strikeslipfault in Turkmenistan, which forms the boundary between stable Eurasia and the eastern parts of theCaspian block. This slip-rate estimate, along with other from the eastern Alborz of NE Iran, allow us todetermine the rates and directions of motion relative to both Iran and Eurasia. Comparison of the presentdayfault slip-rates with cumulative bedrock displacements across the faults, and also with independentgeological estimates of mountain building where available, allow us to comment on the onset of thepresently active deformation in the basin interior and within the mountain ranges that surround it. Despitelarge destructive earthquakes in ۱۹۴۸ in Ashkabad, and a series of deep earthquakes in the eastern Caspianlowlands, the MKDF overall shows an absence of earthquakes both in recent times and in history. Weuncover evidence for large earthquakes that have occurred along the MKDF within the last ۱۰۰۰ years,showing that the MKDF is capable of producing large earthquakes, and also showing that the historicalrecord in this part of Iran is not complete over the Medieval period. We are aided in our study of the MKDFby the very well preserved landscape, which preserves lateral offsets of amounts ranging from single-eventoffsets of ۵-۷ m, through to large-scale cumulative displacements of ~۱ km. By building a histogram ofoffset measurements, and by applying the few Quaternary dates that we have obtained, we are able toproduce a chronology of alluvial fan formation extending over the past ~۱۰۰ ka, which is likely to representregional changes in environment.