EVIDENCE FOR THE RECURRENCE OF LARGE-MAGNITUDE EARTHQUAKES ALONG THE MAKRAN COAST OF IRAN AND PAKISTAN

The presence of raised beaches and marine terraces along the Makran coast indicates episodic uplift of the continental margin resulting from large-magnitude earthquakes. The uplift occurs as incremental steps similar in height to the 1-3 m of measured uplift resulting from the November 28, 1945 (M 8.3) earthquake at Pasni and Ormara, Pakistan. The data support an E-W-trending, active subduction zone off the Makran coast. The raised beaches and wave-cut terraces along the Makran coast are extensive with some terraces 1-2 km wide, 10-15 m long and up to 500 m in elevation. The terraces are generally capped with shelly sandstones 0.5-5 m thick. Wave-cut cliffs, notches, and associated boulder breccia and swash troughs are locally preserved. Raised Holocene accretion beaches, lagoonal deposits, and tombolos are found up to 10 m in elevation. The number and elevation of raised wave-cut terraces along the Makran coast increase eastward from one at Jask, the entrance to the Persian Gulf, at a few meters elevation, to nine at Konarak, 250 km to the east. Multiple terraces are found on the prominent headlands as far east as Karachi. The wave-cut terraces are locally tilted and cut by faults with a few meters of displacement. Long-term, average rates of uplift were calculated from present elevation, estimated elevation at time of deposition, and 14C and U-Th dates obtained on shells. Uplift rates in centimeters per year at various locations from west to east are as follows: Jask, 0 (post-Sangamon); Konarak, 0.031-0.2 (Holocene), 0.01 (post-Sangamon); Ormara 0.2 (Holocene). © 1979.