Amr Elnashai, a Fellow of the Royal Academy of Engineering in the United Kingdom, is the first recipient of the William J. & Elaine F. Hall Endowed Professorship at Illinois and is the director of both the Mid-America Earthquake Center and the George E. Brown Network for Earthquake Engineering Simulation Laboratory at Illinois.
Was the earthquake that affected Hawaii Oct. 15 a typical earthquake?
It takes some time to run a fault-plane solution, define the mechanism and locate the earthquake with regard to local plate boundaries, or faults within a plate. Following media reports is not a good idea. For example, the media indicated that Kobe (Japan) was wiped out after the earthquake of January 1995, whereas there were 6,000 killed out of several millions. Finally, there are no “typical'” earthquakes as such; each is individual and sends us new challenges to try to understand. It is best to wait for more analysis from various leading groups, such as Harvard and others, to work out the mechanism, monitor carefully aftershock activity, perhaps using some more temporary measuring stations, and then see what the media means by “typical.”
If this was, indeed, an undersea earthquake, why did it not cause a tidal wave?
Not all earthquakes create tsunamis. There has to be a large movement of a mass of earth to push the fluid above it. For example, strike-slip earthquakes – those that involve the horizontal movement of one plate with respect to the other – do not move the fluid above it. Usually thrust (collision) earthquakes cause large fluid mass movement. The Asian tsunami was caused by a huge fault, perhaps up to 1000 kilometers long, which broke not only previously dormant parts of the major plate boundary but did indeed break parts that have had earthquakes on them only a few decades ago. The vertical offset on the fault was several meters. The volume of water displaced by a 1,000 kilometer fault of displacement a few meters is massive, and moved toward the shore. No such situation seemed to have existed in Hawaii.
Does an earthquake of this magnitude increase the likelihood of volcanic activity in the islands?
Not necessarily. Some earthquakes are preceded by volcanic activity (for example, the Indonesian earthquake of May 2006, preceded by the eruption of the Mount Merapi volcano), but even then we are not sure they are related. And if they are related, one does not tell us what the other intends to do. So, searching the connection is probably not useful. Earthquakes mostly, but not at all exclusively, occur on plate boundaries, and volcanoes draw their magmatic material from deep fissures often associated with thin crust. So, in principle they co-exist.
