Earthquakes and Ground Motions - Earthquake Engineering for Structural Design - page 221

Dominant
direction

Epicenter

Focus

Figure 7.2 Fault rupture progress

where the Cocos plate subducts the North American plate (Lowry et al, 2001). The
different segments of this plate boundary are very active in different periods. There
is also a gap, named Guerrero gap, where for a long time no earthquakes were
recorded. The aspects can be observed along the North Anatolian fault (see Fig.
3.4). Generally, the gaps are often considered to be the sites of the next great
earthquakes. A way to explain these regional variations in seismicity along plate
boundaries is to introduce the fault asperities and barriers, whose size varies from
one place to another.

7.2.2 Asperities and Barriers

Asperity implies the inequality or roughness of the surface of the body, whereby
some parts of it stick out beyond the rest, increasing the surface friction of any
object moving over it (Wikipedia, nd). In Seismology, this term is used to describe
the heterogeneity of a fault. Asperity is the small site on a fault surface of higher
strength than the surrounding, where stress concentrates prior to the fault rupture.