Forecasting of the first hour aftershocks by means of the perceived magnitude

Abstract

The majority of strong earthquakes takes place a few hours after a mainshock, promoting the interest for a real time post-seismic forecasting, which is, however, very inefficient because of the incompleteness of available catalogs. Here we present a novel method that uses, as only information, the ground velocity recorded during the first 30 min after the mainshock and does not require that signals are transferred and elaborated by operational units. The method considers the logarithm of the mainshock ground velocity, its peak value defined as the perceived magnitude and the subsequent temporal decay. We conduct a forecast test on the nine M ≥ 6 mainshocks that have occurred since 2013 in the Aegean area. We are able to forecast the number of aftershocks recorded during the first 3 days after each mainshock with an accuracy smaller than 18% in all cases but one with an accuracy of 36%.

Improvements to seismicity forecasting based on a Bayesian spatio-temporal ETAS model

“…( 14) is calculated piece-wise by summing over the sub-intervals [t i-1 , t i ] (where i = 2:N o ) and the last interval [ t N o , T start ] (where t N o is the arrival time of the event N o ) as follows (see also Eq. (10) and Eq. (11);…”

“…Within the first days elapsed after the occurrence of an earthquake and in the presence of an ongoing seismic sequence, emergency decision-making can benefit enormously from the short-term operational seismicity forecasts [1][2][3][4][5][6][7][8][9][10] . The Epidemic Type Aftershock Sequence (ETAS) model is a widely used stochastic model to describe earthquake temporal 11 and spatio-temporal 12 occurrence and clustering of seismicity within a seismic sequence (see also [13][14][15] ).…”

Post Seismic Catalog Incompleteness and Aftershock Forecasting

“…In this section, we present two methods which have been developed in order to provide real-time aftershock forecasting: The Omi method [7,9,10] and the Lippiello method [16,17]. The idea of both methods is to extrapolate the parameters of the OU law, or more generally of the ETAS model, by means of an automatic procedure which uses the information available up to a time T 2 after the mainshock.…”

“…Summarizing, results of Figure 11 clearly show that the Lippiello method performs much better than the generic model providing a reasonable aftershock forecasting. Very recently, Lippiello et al [17] proposed a more efficient procedure, still based on the agreement between µ th (t) and µ e (t), which produces even more accurate STA forecasting. (6) using the average values obtained in Reference [55].…”

“…These approaches, however, are not simple to be implemented in real-time automatic procedures for aftershock forecasting. This is the topic of Section 6, which presents two different procedures developed to provide accurate STA forecasting, several minutes after the occurrence of a mainshock: the Omi et al method [7,9,10] and the Lippiello et al method [16,17]. The test of these two methods in retrospective studies is presented in Section 6 and final conclusions are drawn in the last section.…”