Statistical Analysis of Pre-Earthquake ULF Geomagnetic Anomalies: Dependency on Earthquake Catalogs
Abstract
Since Fraser-Smith et al. [1990] reported anomalies in Ultra-Low Frequency (ULF) magnetic data prior to the 1989 Loma Prieta earthquake, ULF signals are often presented as some of the most viable candidates in the search for earthquake precursors. However, there is still no consensus as of when these ULF perturbations should happen, with examples in the literature ranging from several weeks to several hours prior to the associated seismic events. Studying the statistical significance of such anomalies for multiple earthquakes therefore seems like a pertinent idea. This path was recently followed by Han et al. [2014], who performed a Statistical Epoch Analysis (SEA) of ULF phenomena by processing 10 years of data acquired at the Japanese geomagnetic observatory of Kakioka between 2001 and 2010. In order to better understand the mechanisms underlying alleged pre-earthquake ULF anomalies, we think that it would be fruitful to test a similar processing strategy against other datasets. We therefore independently wrote a Python script following the workflow described in Han et al. [2014] and tried reproducing their results to validate our program. When considering the same list of "earthquake days" as the one provided in their study, we also found that ULF magnetic anomalies are more likely to appear before sizable earthquake events rather than after them. However, when using different catalogs, such as those issued by USGS or ISC, we found our results to vary substantially. With this sensitivity study we hope to raise awareness about how using different catalogs may impact the results of pre-earthquake analyses. As a good practice, we suggest testing any method against several catalogs, regardless of whether considering ULF signals or other physical phenomena.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMNH53C0826W
- Keywords:
-
- 2427 Ionosphere/atmosphere interactions;
- IONOSPHERE;
- 4302 Geological;
- NATURAL HAZARDS;
- 7223 Earthquake interaction;
- forecasting;
- and prediction;
- SEISMOLOGY;
- 7999 General or miscellaneous;
- SPACE WEATHER