Paleoearthquake deformations recorded by magnetic variables

Faults and related deformational structures give evidence of earthquakes in the past. The ground shaking at high-magnitude seismic events usually generates liquefaction; the higher seismic magnitude, the larger area of liquefaction. We can now demonstrate that it is possible to discriminate between plastic and liquefied deformations with magnetic methods. Besides, it is possible to record internal crypto-deformations not visibly observed. This offers new means of recording past earthquakes. Fine particles carrying the magnetic remanence are shown to move, rotate and re-align with respect to the prevailing geomagnetic field direction or in response to the applied shaking forces. We call this seismomagnetization. This implies that paleoseismics may generate excursion-like paleomagnetic signals despite the absence of visible deformation structures.