Evidence for the recurrence of large-magnitude earthquakes along the Makran coast of Iran and Pakistan

Abstract

(Accepted for publication June 8, 1978) ABSTRACT: Page, W.D., Alt, J.N., Cluff, L.S. and Plafker, G., 1979. Evidence for the recurrence of large-magnitude earthquakes along the Makran coast of Iran and Pakistan. In: C.A. Whitten, R. Green and B.K. Meade (Editors), Recent Crustal Movements, 1977. Tectonophysics, 52: 533-547. 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 14 C 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).