Check this out, from 2016...

Precursor analysis of ionospheric GPS-TEC variations before the 2010 M7.2 Baja California earthquake

Total electron content (TEC) data obtained from receivers of global navigation satellite systems (GNSSs) are increasingly being used to detect pre-earthquake ionospheric anomalies. In this study, the pre-earthquake ionospheric anomalies that occurred before the 2010 Baja California (32.128° N, 115.303° W, 4 April 2010, 22:40:42 UTC, Mw = 7.2) earthquake were investigated using TEC from Global Positioning System–Total Electron Content (GPS-TEC) data from five International GNSS Service (IGS) stations (SIO3, GOL2, QUIN, AMC2 and DRAO) near the epicentre and one IGS station (GRAZ) away from the epicentre. An analysis of the time of occurrence and duration yielded the following conclusions: both positive and negative anomalies are likely to occur and earthquake-related ionospheric anomalies occurred one to five days before the associated earthquake. The potential causes of these results were discussed. The observed anomalous variations in GPS-TEC may be attributed to the earthquake.

[link to www.tandfonline.com]