Question

Foreshocks are often recorded in which phase?

(a) Preparatory phase

(b) Rupture phase

(c) Post failure phase

(d) Tertiary phase

The question was posed to me during an interview.

This question is from Causes of Earthquakes in section Earthquakes of Engineering Geology

Answer 1

The correct option is (a) Preparatory phase

To explain I would say: The preparatory phase is the phase in which a non-hydrostatic stress field is created in a certain region around a fault; the direction of the preparatory phase is to ultimately define the size of the actual earthquake. A number of “foreshocks” are often recorded during this phase.