Changepoint analysis of Vp/Vs ratio time-series using a trans-dimensional McMC algorithm: an application to the Alto-Tiberina seismic network (Northern Apennines, Italy)

Author(s)

Nicola Piana Agostinetti, Giulio Poggiali, Raffaele Di Stefano, Lauro Chiaraluce

Abstract

Time-series of Vp/Vs ratio have been used to track local changes in

elastic properties of the rock volumes associated, e.g., to fluid

migration within a fault system. A value of Vp/Vs ratio can be computed

from travel-time of P- and S- waves generated from a single local event

and it is representative of the value of the Vp/Vs ratio for the rocks

traversed by the seismic ray, between the source and the receiver. It is

straightforward, during a seismic sequence, to generate time-series of

Vp/Vs ratio for colocated events and a single station. Such time-series

should be able to "monitor" the variations of elasticity in the rock

volume. Due to the expected tiny changes in P- and S- wave velocity, the

evaluation of Vp/Vs ratio time-series has been problematic in the past,

and subjective choices about, e.g. time-averaging scheme applied or

events selection for constructing the time-series, have been proven to

strongly affect the outcomes of the analysis. In this contribution, we

present the application of a new methodology for a statistical

evaluation of changes in Vp/Vs ratio time-series. The new methodology

belongs to the wide class of "changepoint analysis" algorithms and is

developed in the framework of Bayesian inference. The posterior

probability distribution (PPD) of the changepoint locations is obtained

using a trans-dimensional Markov chain Monte Carlo (trans-D McMC)

algorithm, where the number (if any) of changepoints is directly

dictated by the data themselves. We apply the new algorithm to the

seismic catalogue produced by the Alto-Tiberina seismic network

(Northern Apennines, Italy). Thanks to the huge amount of seismic data

available, we are able locate the occurrence of changepoints in the

Vp/Vs ratio time-series. Changepoint time- and space- distributions are

compared with the occurrence of Mw2+ seismic events in the area.

Organisation(s)

Department of Geology

External organisation(s)

Dublin Institute for Advanced Studies, Istituto Nazionale di Fisica Nucleare (INFN), Roma

Pages

13599

Publication date

04-2018

Peer reviewed

Yes

Austrian Fields of Science 2012

105102 General geophysics

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