The first regional swath-bathymetry survey of the Makran accretionary wedge
revealed a sinistral strike-slip fault, named herein the Some fault, obliq
uely crossing the wedge and continuing into the abyssal plane. This fault s
eparates the western part of the Makran subduction zone where plate boundar
y events are absent from the eastern part that does show plate boundary sei
smicity; most events are concentrated along the Some fault. Little Murray R
idge (a basement high) and related magnetic anomalies are offset along the
Some fault. Together, these observations identify the newly discovered Some
strike-slip fault as a plate boundary that has been active similar to 2 m.
y. This finding suggests that what has been considered the northeasternmost
part of the Arabian plate is actually a separate microplate, named herein
the Ormara plate, the formation of which resulted from tearing of the Arabi
an plate along the Some fault. With this concept, the different dips of the
downgoing plate below the western and eastern parts of the Makran margin a
nd the related different distances between the trench and Quaternary are vo
lcanic centers can be unequivocally explained.