Short term and short range seismicity patterns in different seismic areas of the world

Citation
R. Console et al., Short term and short range seismicity patterns in different seismic areas of the world, NAT HAZARDS, 19(2-3), 1999, pp. 107-121
Citations number
12
Categorie Soggetti
Earth Sciences
Journal title
NATURAL HAZARDS
ISSN journal
0921030X → ACNP
Volume
19
Issue
2-3
Year of publication
1999
Pages
107 - 121
Database
ISI
SICI code
0921-030X(199905)19:2-3<107:STASRS>2.0.ZU;2-K
Abstract
The aim of this work is to quantitatively set up a simple hypothesis for oc currence of earthquakes conditioned by prior events, on the basis of a prev iously existing model and the use of recent instrumental observations. A si mple procedure is presented in order to determine the conditional probabili ty of pairs of events (foreshock-mainshock, mainshock-aftershock) with shor t time and space separation. The first event of a pair should not be an aft ershock, i.e., it must not be related to a stronger previous event. The Ita lian earthquake catalog of the Istituto Nazionale di Geofisica (ING) (1975- 1995, M greater than or equal to 3.4), the earthquake catalog of the Japan Meteorological Agency (JMA) (1983-1994, M greater than or equal to 3.0) and that of the National Observatory of Athens (NOA) (1982-1994, M greater tha n or equal to 3.8) were analyzed. The number of observed pairs depends on s everal parameters: the size of the space-time quiescence volume defining no naftershocks, the inter event time, the minimum magnitude of the two events , and the spatial dimension of the alarm volume after the first event. The Akaike information criterion has been adopted to assess the optimum set of space-time parameters used in the definition of the pairs, assuming that th e occurrence rate of subsequent events may be modeled by two Poisson proces ses with different rates: the higher rate refers to the space-time volume d efined by the alarms and the lower one simulates earthquakes that occur in the nonalarm space-time volume. On the basis of the tests carried out on th e seismic catalog of Italy, the occurrence rate of M greater than or equal to 3.8 earthquakes followed by a M greater than or equal to 3.8 mainshock w ithin 10 km and 10 days (validity) is 0.459. We have observed, for all thre e catalogs, that the occurrence rate density lambda for the second event of a couple (mainshock or aftershock) of magnitude M-2 subsequent to a nonaft ershock of magnitude M-1 in the time range T can be modeled by the followin g relationship: lambda (T, M-2) = 10(a)' (+ b(M1) (- M2)) with b varying fr om 0.74 (Japan) to 1.09 (Greece). The decrease of the occurrence rate in ti me for a mainshock after a foreshock or for large aftershocks after a mains hock, for all three databases, obeys the Omori's law with p changing from 0 .94 (Italy) to 2.0 (Greece).