The 1999 Mw 7.7 Chi-chi earthquake in Taiwan produced spectacular surface faulting, with vertical displacements of up to 8 m on the Chelungpu fault. The large amount of fault slip at or near the surface provides a unique opportunity to study first-hand the physical mechanisms involved in faulting during large earthquakes. Intriguingly the portions of the fault in the north that had the largest amount of displacement produced relatively low levels of damage. The slip and slip velocity were very large, but the high-frequency acceleration was relatively low, suggesting that somehow the northern portion of the fault slipped rather smoothly
This clearly-recorded behavior of the Chleungpu fault provides clues for unraveling an important research topic in seismology: What physical properties or dynamic processes control the distribution of large slip during an earthquake? It is well known that the amount of slip during a large earthquake varies considerably at different locations along the fault. However, little is known about why this is so. Understanding what controls the amount of slip that occurs on the fault would improve our understanding of the earthquake rupture process.