Low detection capability of global earthquakes after the occurrence of large earthquakes: investigation of the Harvard CMT catalogue

Wang

2017

Earth Planets Space

This study investigates the missing data problem in the Japan Meteorological Agency catalog of the Kumamoto aftershock sequence, which occurred since April 15, 2016, in Japan. Based on the assumption that earthquake magnitudes are independent of their occurrence times, we replenish the short-term missing data of small earthquakes by using a bi-scale transformation and study their influence on the maximum likelihood estimate (MLE) of the epidemic-type aftershock sequences (ETAS) parameters by comparing the analysis results from the original and the replenished datasets. The results show that the MLEs of the ETAS parameters vary when this model is fitted to the recorded catalog with different cutoff magnitudes, while those MLEs remain stable for the replenished dataset. Further analysis shows that the seismicity becomes quiescent after the occurrence of the second major shock, which can be regarded as a precursory phenomenon of the occurrence of the subsequent M J 7.3 mainshock. This relative quiescence is demonstrated more clearly by the analysis of the replenished dataset.

Section: Introductionmentioning

confidence: 99%

Data completeness of the Kumamoto earthquake sequence in the JMA catalog and its influence on the estimation of the ETAS parameters

Zhuang

Wang

2017

Earth Planets Space

“…For the purpose, we must consider the statistical feature of incompletely detected aftershocks. To model the incomplete detection of earthquakes, previous studies18192021 introduced the detection rate function of magnitude, the probability at which each underlying earthquake is detected. The detection rate of an earthquake clearly depends on its magnitude such that smaller (larger) earthquakes are detected with a lower (higher) probability.…”

Section: Resultsmentioning

confidence: 99%

“…The detection rate of an earthquake clearly depends on its magnitude such that smaller (larger) earthquakes are detected with a lower (higher) probability. The detection rate function of the magnitude is suitably represented by the cumulative distribution function of the normal distribution Φ( M | μ , σ ), where μ represents the magnitude with a 50% detection rate, and σ represents a partially detected magnitude range18192021. By means of suitable estimate of the detection rate function, we can estimate the occurrence rates of the underlying earthquakes from given data of incompletely detected earthquakes.…”

Section: Resultsmentioning

confidence: 99%

“…This function works well if the hypocenter detection is based on an enough number of homogeneously located seismic stations181920. There may be other possible detection functions, such as the logistic function19 and the exponential detection function21, dependent on configuration of seismic networks.…”

Section: Discussionmentioning

confidence: 99%

“…A similar Bayesian model for estimating the time-dependent detection rate was implemented using cubic spline19 or broken-line-type parameterization20. The present state-space representation of the Bayesian model enables adaptive updating of the prediction in real time.…”

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Forecasting large aftershocks within one day after the main shock

Omi

Hirata

et al. 2013

Sci Rep

Forecasting the aftershock probability has been performed by the authorities to mitigate hazards in the disaster area after a main shock. However, despite the fact that most of large aftershocks occur within a day from the main shock, the operational forecasting has been very difficult during this time-period due to incomplete recording of early aftershocks. Here we propose a real-time method for efficiently forecasting the occurrence rates of potential aftershocks using systematically incomplete observations that are available in a few hours after the main shocks. We demonstrate the method's utility by retrospective early forecasting of the aftershock activity of the 2011 Tohoku-Oki Earthquake of M9.0 in Japan. Furthermore, we compare the results by the real-time data with the compiled preliminary data to examine robustness of the present method for the aftershocks of a recent inland earthquake in Japan.

Estimating the ETAS model from an early aftershock sequence

Omi

Geophysical Research Letters

Hirata

et al. 2014

Forecasting aftershock probabilities, as early as possible after a main shock, is required to mitigate seismic risks in the disaster area. In general, aftershock activity can be complex, including secondary aftershocks or even triggering larger earthquakes. However, this early forecasting implementation has been difficult because numerous aftershocks are unobserved immediately after the main shock due to dense overlapping of seismic waves. Here we propose a method for estimating parameters of the epidemic type aftershock sequence (ETAS) model from incompletely observed aftershocks shortly after the main shock by modeling an empirical feature of data deficiency. Such an ETAS model can effectively forecast the following aftershock occurrences. For example, the ETAS model estimated from the first 24 h data after the main shock can well forecast secondary aftershocks after strong aftershocks. This method can be useful in early and unbiased assessment of the aftershock hazard.