Some seismicity may be affected by weather due to wind, tidal surge and air pressure systems effects of  the continental mass compared with adjoining plate masses. During the tropical storm season in the Northern Hemisphere we keep an eye on tropical storms which may affect seismicity according to our models.  Currently the following tropical storms appear to have potential to affect seismicity in the coming week:





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TS    ANDRES   2021-05-13  00:00 UT  16.0N  112.7W  85  kts  South of Jalisco,, Mexico    


Tropical storm Andres continued in the area south of Jalisco, Mexico with winds up to 85 kts.  Little impact on regional seismicity is expected with this storm but an M 5.1 in Michoacan today was probably promoted by stresses from this storm. The antipode of this storm is at 17S 67E in the South Indian Ridge. A moderate to strong earthquake in this area is possible. This longitude is also near the maximum tidal stress with the current new moon.




The new moon will arrive on May 11, 2021 at 19:00 UT. Longitudes which are at local solar noon at this hour are near 105 West and those at local solar midnight near 75 East longitude. In the west these include areas of central and Western U.S. and Canada and western Mexico as well as portions of the East Pacific Rise. In the east area near 75E include Afghanistan, India, Hindu Kush, Iran and eastern Indonesia and portions of the mid-Indian ridges. These regions are expected to see enhanced seismicity during the coming week. Other tidally promoted seismicity may occur elsewhere and is most likely near local solar midnight and noon when tidal stresses are generally maximized.


May 13, 2021  is the second day after the beginning of the new lunar month.  Regions most likely to experience tidal triggering on this day (With associated magnitude ranges; the percent change in seismicity rate over background seismicity rate on this day of the lunar month; statistical z-value and significance level) are:


Region Magnitude range %change z-value Significance level


Idaho MB>=1.0 15 1.9 0.05

New Zealand MB>=4.0 17 2.0 0.05

NW Europe MB>=4.0 9 2.0 0.05

So South America MB>=4.0 36 4.0 0.01

Central California MB>=2.0 7 1.9 0.05

Mammoth Lakes MB>=2.0 48 2.4 0.04

Mammoth Lakes MB>=3.0 26 2.9 0.01



Regions expected to experience reverse triggering (i.e. they are unlikely to experience a significant event at this period of the lunar cycle) are:



Region Magnitude range %change z-value Significance level


Global MB>=6.0 -14 -2.3 0.04

Siberia MB>=4.0 -45 -2.4 0.04



Region Magnitude range %change z-value Significance level


No regions