Assessing the Dependency Between Magnitudes of Earthquakes and Magnitudes of Their Aftershocks

• Activity Number: 566
• Type: Contributed
• Date/Time: Wednesday, August 1, 2012 : 2:00 PM to 3:50 PM
• Sponsor: Section on Nonparametric Statistics
• Author(s): Kevin Nichols*+
• Companies: California State University Fullerton
• Keywords: ETAS ; MISD ; Aftershock ; Expectation Maximization ; Magnitude ; Dependency

Abstract

Current assumptions on the level of dependency between the magnitudes of earthquakes and the magnitudes of their aftershocks vary significantly, ranging from assumed independence for models like Epidemic type Aftershock-Sequence (ETAS) to assumed positive correlation, at least for the events leading up to the largest earthquakes, for models like Accelerated Moment Release (AMR). (Marsan 2008) developed a method for model independent stochastic declustering (MISD) of a multi-dimensional Hawkes self-exciting process, or as is the case here, earthquake activity. Repeated application of MISD to a global earthquake catalog allows for estimates with confidence bounds for the average magnitude of an aftershock conditioned upon the magnitude(s) of the earthquake(s) that caused the aftershock. Results based on a global CMT earthquake catalog indicate that the magnitudes of aftershocks are dependent on the magnitudes of the earthquakes that cause them and indeed larger than average earthquakes are more likely to trigger larger than average aftershocks.