活断層から発生する地震の規模と周期について

抄録

The recurrence interval (R) of earthquakes from a given fault-segment is related to the long-term slip-rate (S) and the displacement accompanying an earthquake (D). The relation is expressed as R=D/S [WALLACE (1970)], when aseismic fault creep is disregarded. D has a relation with the earthquake magnitude M as logD(meter)=0.6M-4.0 for Japanese inland earthquakes. Then, the relation R to M is expressed as logR=0.6M-4.0-logS.
It is proposed here that a given fault-segment has a constant value in D through time during late Quaternary period. Values D and M may be different between different faults or segments, but there is a proper value D₀ or M₀ for a given fault or its segment. Historic records on Japanese earthquakes seem consistent with this assumption. D₀ or M₀ is obtained from data of historic earthquakes or from a unit offset of geologic references.
Fault length L is proportional to a dimension of strain domain, and it represents the maximum magnitude from the fault. The relation of L to earthquake magnitude M is logL(kilometer)=0.6M-2.9 for Japanese inland earthquakes. Then, maximum magnitude M_L from a fault is expressed as M_L=(1/0.6)logL+4.85.
When a given fault or its segment has no earthquake during at least t years up to the present, the accumulated earthquake energy during t years is expressed as M_t=(1/0.6)log(t·S)+6.67.
Thus, a probable maximum magnitude M_max from a given fault or its segment is expressed as M_t<M_max<M_L. Examples of the above procedure and its result are described.