Active faults those with recent offset in the last 10,000 years. Inactive faults

CO 01

Fig. 1.01

Reactivated Faults and earthquakes

• Most shallow earthquakes occur on active faults

• those with recent offset in the last 10,000 years.

• Inactive faults do not have observed earthquakes or evidence of slip in the last 1.6 million years.

• However, some faults have large earthquakes only once every thousands of years. Reactivated faults form when movement occurs along formerly inactive faults due to a change in stress.

• Deformation in the New Madrid seismic zone in the central USA is an example of fault reactivation.

• Rift structures that formed about 500 million years ago have been responding to recent stresses in the mid-continent