Why Wasn There a Larger Tsunami from the Magnitude 8.7 March 28, 2005, Sumatra Earthquake?
By Eric L. Geist April 2005 in this issue: previous story | next story Above: Regional map of the area affected by the December and March earthquakes and tsunamis. Stars indicate epicenters for both earthquakes. Ovals indicate approximate areas of energy concentration (high slip) for the two earthquakes (gray, December; yellow stripes, March). Large arrows indicate approximate directions of tsunami-wave focusing for the two events. Thick red line shows sea-floor trace of the interplate thrust fault at the Sumatra-Andaman subduction zone. [larger version] The question many people asked after the magnitude 8.7 March 28, 2005, earthquake was “Why wasn’t there a tsunami?” To start with, there was a tsunami generated by this earthquake, which is clearly evident from most tide-gauge stations throughout the Indian Ocean (see compilation at University of Hawai’i Sea Level Center). For example, a tide gauge at Malé in the Republic of Maldives, south of India, recorded a tsunami about 20 cm high
