The Largest Expected Earthquake Magnitudes in Japan: The Statistical Perspective

Abstract

Earthquake catalogs are probably the most informative data source about spatiotemporal seismicity evolution. The catalog quality in one of the most active seismogenic zones in the world, Japan, is excellent, although changes in quality arising, for example, from an evolving network are clearly present. Here, we seek the best estimate for the largest expected earthquake in a given future time interval from a combination of historic and instrumental earthquake catalogs. We extend the technique introduced by Zöller et al. (2013) to estimate the maximum magnitude in a time window of length T f for earthquake catalogs with varying level of completeness. In particular, we consider the case in which two types of catalogs are available: a historic catalog and an instrumental catalog. This leads to competing interests with respect to the estimation of the two parameters from the Gutenberg-Richter law, the b-value and the event rate λ above a given lower-magnitude threshold (the a-value). The b-value is estimated most precisely from the frequently occurring small earthquakes; however, the tendency of small events to cluster in aftershocks, swarms, etc. violates the assumption of a Poisson process that is used for the estimation of λ. We suggest addressing conflict by estimating b solely from instrumental seismicity and using large magnitude events from historic catalogs for the earthquake rate estimation. Applying the method to Japan, there is a probability of about 20% that the maximum expected magnitude during any future time interval of length T f 30 years is m ≥ 9:0. Studies of different subregions in Japan indicates high probabilities for M 8 earthquakes along the Tohoku arc and relatively low probabilities in the Tokai, Tonankai, and Nankai region. Finally, for scenarios related to long-time horizons and high-confidence levels, the maximum expected magnitude will be around 10.

Determination of Mmax from Background Seismicity and Moment Conservation

“…The largest earthquake of which we are aware that took place in this location is the 2011 M w 9 Tohoku-Oki event, so here we have a high lower bound for M max . Previous estimates for M max varied from 9 (McCaffrey, 2008, using scaling relations and fault segment lengths) to 10 (if confidence limits are high) (Zöller et al, 2014, using the tapered GR distribution, but not conservation of moment). Using the theory of extreme values, Pisarenko et al (2010) found the absolute M max to be 9:57 0:86 for Japan.…”

Data‐Driven Seismic‐Hazard Models Prepared for a Seismic Risk Assessment in the Dead Sea Region

“…In addition, the observed rate estimated from the complete part of the Uhrhammer catalog since 330 is shown. Acknowledging concerns about assigning a maximum magnitude (Holschneider et al, 2011;Zöller et al, 2013Zöller et al, , 2014, we estimated a maximum magnitude using the Bayesian estimator by Kijko (2004) of M w 8. Inserting this estimate into the nontruncated version of the Gutenberg-Richter relation we obtained, we can estimate an average return period of an event larger than M w 8 as 660 years (Grünthal catalog; Uhrhammer catalog 1200) for the whole region.…”

Comment on Pisarenko et al., “Characterization of the Tail of the Distribution of Earthquake Magnitudes by Combining the GEV and GPD Descriptions of Extreme Value Theory”

“…Pisarenko et al decluster the earthquake catalog and use only the main events to provide a homogeneous Poisson process with independent magnitudes similar to e.g. Zöller et al (2014). But a homogeneous Poisson process is not a necessary condition for applying GEVD and GPD.…”