### On the Potential Duration of the Aftershock Sequence of the 2018 Anchorage Earthquake

By: Andrew J. Michael**

                            https://doi.org/10.3133/ofr20181195

#### Links

-                                                                                                                             Document:                                                                                                                                                                                                                                                  **Report**                                                                                                     (300 KB pdf)                                                                                                                                     
- Download citation as:  RIS                         |                         Dublin                            Core

#### Abstract

First posted December 21, 2018

**For additional information, contact:**
Contact Information,Earthquake Science CenterU.S. Geological Survey345 Middlefield Road, MS 977Menlo Park, CA 94025

Currently, an aftershock sequence is ongoing in Alaska after the magnitude 7.0 Anchorage earthquake of November 30, 2018. Using two scenarios, determined with observations as of December 14, 2018, this report estimates that it will take between 2.5 years and 3 decades before the rate of aftershocks decays to the rate of earthquakes that were occurring in this area before the magnitude 7.0 mainshock. All of the time estimates have significant uncertainty owing to different scenarios of how the sequence may decrease over time and could also change if a large aftershock occurs. The report also estimates the amount of time after the mainshock until the annual probability of magnitude 5 or greater and 6 or greater aftershocks—which could cause additional damage—decreases to 50, 25, 10, and 5 percent. For instance, the probability of one or more magnitude 6 or greater aftershocks in the following year decreases to 10 percent between 7 and 250 days after the mainshock. The same probability for magnitude 5 or greater earthquakes is reached between 500 and 7,000 days after the mainshock.

#### Suggested Citation

Michael, A.J., 2018, On the potential duration of the aftershock sequence of the 2018 Anchorage earthquake: U.S. Geological Survey Open-File Report 2018–1195, 6 p., https://doi.org/10.3133/ofr20181195.

ISSN: 2331-1258 (online)

#### Table of Contents

- Abstract
- Introduction
- 2018 Anchorage Earthquake Aftershock Sequence and Earlier Earthquakes
- Modeling The Aftershock Sequence
- Conclusions
- Acknowledgments
- References
- Appendix 1

Part or all of this report is presented in Portable Document Format                        (PDF). For best results viewing and printing PDF documents, it is recommended that you download                        the documents to your computer and open them with Adobe Reader. PDF documents opened from your                        browser may not display or print as intended. Download the latest version of Adobe Reader, free of charge. More information                        about viewing, downloading, and printing report files can be found at the common download problems FAQ.