EARTHQUAKES OF MEXICO Table 1. Mexican Tectonics Area Baja
Volcanic Province
Rio Grande San Andreas Rivera Pacific
Number Recorded
11 24
3 2 5 1
Magnitude (Average)
4.2 - 6.9 (5) 4 - 6.9 ( 5.6)
4.3 - 4.4 (4.35) 7.2
4.8 - 6.3 (5.6) 6.3
Tectonic Elements Observed from Seismometer
The letter “M” represents the USGS moment magnitude and “D” is depth of focus in the following figures.
Volcanic Province, Figures 5 – 7
According to plate tectonics, the Volcanic Province is linked to the Middle America Trench subduction zone by earthquake activity on the subducting Cocos Plate. One would think that earthquake activity would be observed at the subduction of the Cocos Plate beneath the North American Plate at the Middle America Trench. In fact, I have only recorded earthquakes from adjacent Guatemala and Nicaragua (a caveat is that the EQ-1 is not sensitive to earthquakes of magnitudes less than about 4 from such distances). But, earthquakes were recorded 300 km inland. Prominent active volcanoes form the Volcanic Province, including El Chichon, Vulcan de San Martin, Colma, Ceboruco, and the famous volcano Paraicuten volcano born in 1943 and active to 1951, (Bullard, 1986). However, these volcanoes usually do not cause large earthquakes. The large earthquakes in this area originate from a different source, termed “flat slab subduction,” per the subsequent discussion.
Depth (Average) Distance (Km)
10 - 24 (10.9)
9 - 525 (55)*
9.8 - 10.2 10
* Does not include earthquake at 525 km depth. Type 1461 - 1622 (1605) Spread Center 880 - 2029
870 - 880 1750
2159 Subduction Rift Transform
4.8 - 53.5(22.4) 1840 - 1907 (1864) Transform 11.3
Intra-Plate?
Transform Faults, Figures 8 – 10
The San Andreas Fault is a major right-lateral transform fault separating the North American plate from the Pacific plate. I recorded one major earthquake on the San Andreas Fault in Mexico.
Figure 8. San Andreas Fault, major earthquake of Mag. 7.2 with aftershocks. April 2010, M 7.2, D 10 km.
Rivera Micro-Plate Transform, Figures 9 and 10
The Rivera Plate is a small micro-plate located off coastal Mexico. It is believed to have separated from the Cocos Plate about 5-10 million years ago (DeMets, 2000). Plate tectonic theory states that earthquakes occur only between active spreading centers along the corresponding transform faults (Cox and Hart, 1986). As seen in Figure 1, earthquakes in this area only occur along a small linear area, and are con- fined to the area between spreading centers along the Rivera Transform Fault.
Figure 5. Oaxaca, July 9, 2011. M 5.6, D ?
Figure 6. Guerrero. April 27, 2008. M 6.9, D 40 km.
Figure 7. July 7, 2014. M 6.9, D 37.3 km. Note scale difference, whole page not magnified.
Figure 9. Dec. 17, 2010. M 5.1, D 10.8 km.
Figure 10. Nov. 1, 2011. M 6.3, D 5 km.
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