Is there a near-field for small-to-moderate magnitude earthquakes?

The major hazard posed by earthquakes is often thought to be due to moderat e to large magnitude events. However, there have been many cases where eart hquakes of moderate and even small magnitude have caused very significant d estruction when they have coincided with population centres. Even though th e area of intense ground shaking caused by such events is generally small, the epicentral motions can be severe enough to cause damage even in well-en gineered structures. Two issues are addressed here, the first being the ide ntification of the minimum earthquake magnitude likely to cause damage to e ngineered structures and the limits of the near-field for small-to-moderate magnitude earthquakes. The second issue addressed is whether features of n ear-field ground motions such as directivity, which can significantly enhan ce the destructive potential, occur in small-to-moderate magnitude events. The accelerograms from the 1986 San Salvador (El Salvador) earthquake indic ate that it may be unconservative to assume that near-field directivity eff ects only need to be considered for earthquakes of moment magnitude M 6.5 a nd greater.