第25回統計地震学セミナー

日時(Date)

2012年5月18日（金）/ 18 May 2012 (Friday)

時間(Time)

16:00-17:00

場所
(Location)

統計数理研究所 D312A号室 /
Room D312A @ Institute of Statistical Mathematics

講演題目(Title)

Earthquake occurrence: emulation and climate forcing

講演者
(Speaker)

Prof. Serge Guillas
(Reader (Associate Professor) in Statistics, University College London, Department of Statistical Science)

概要
(Abstract)

In earthquake occurrence studies, the so-called q value can be considered both as one of the parameters describing the distribution of interevent times and as an index of non-extensivity. Using simulated datasets, we compare four estimators, based on principle of maximum entropy, method of moments, maximum likelihood, and probability weighted moments (PMW) of the parameters of the distribution of inter-events times, assumed to be a generalized Pareto distribution. We then use the unbiased version of PWM estimators to compute the q value for the distribution of inter-event times in a realistic earthquake catalogue simulated according to the epidemic type aftershock sequence (ETAS) model. Finally, we use these findings to build a statistical emulator of the q values of ETAS model. We employ treed Gaussian processes to obtain partitions of the parameter space so that the resulting model respects sharp changes in physical behaviour. The emulator is used to understand the joint effects of input parameters on the q value, exploring the relationship between ETAS model formulation and distribution of inter-event times. We then present statistical evidence for a temporal link between variations in the El Niño-Southern Oscillation (ENSO) and the occurrence of earthquakes on the East Pacific Rise (EPR). We adopt a zero-inflated Poisson regression model to represent the relationship between the number of earthquakes in the Easter microplate on the EPR and ENSO (expressed using the southern oscillation index (SOI) for east Pacific sea-level pressure anomalies) from February 1973 to February 2009. We also examine the relationship between the numbers of earthquakes and sea levels, as retrieved by Topex/Poseidon from October 1992 to July 2002. We observe a significant positive influence of SOI on seismicity: positive SOI values trigger more earthquakes over the following 2 to 6 months than negative SOI values. There is a significant negative influence of absolute sea levels on seismicity (at 6 months lag). We propose that increased seismicity is associated with ENSO-driven sea-surface gradients (rising from east to west) in the equatorial Pacific, leading to a reduction in ocean-bottom pressure over the EPR by a few kilopascal. This relationship is opposite to reservoir-triggered seismicity and suggests that EPR fault activity may be triggered by plate flexure associated with the reduced pressure.