2 very strong dangerous earthquakes in the Gulf of California – Minor damage reported in Guaymas

Last update: April 13, 2012 at 9:58 am by By Armand Vervaeck and James Daniell

Most important Earthquake Data:
Magnitude : 6.8-6.9
UTC Time : Thursday, April 12, 2012 at 07:15:48 UTC
Local time at epicenter : Thursday, April 12, 2012 at 12:15:48 AM at epicenter
Depth (Hypocenter) : 10.3 km
Geo-location(s) :
134 km (83 miles) NE (48°) from Guerrero Negro, Baja California Sur, Mexico
162 km (101 miles) W (268°) from La Doce, Sonora, Mexico

Update 13/04 – 09:54 UTC
The staff of Civil Protection, Urban Infrastructure and SIUE (Ministry of Urban Infrastructure and Ecology) is conducting currently an inspection in the Guaymas area.
The local head of Civil Protection, Leon Gerardo Soto reported that home owners in the greater Guaymas area have calles the Civil Protection to report damage on their houses.
Regarding the City Hall (Palacio Municipal), he said that new cracks were found at the main entrance.

Palacia Municipal de Guaymas – Image courtesy english.realmexico.info

Update 21:12 UTC
* Cracks on walls in Guaymas,Sonora : People were calling newspapers and local media to reportdamages in their houses. El Palacio Municipal (Municipal Palace ,local government building) reported cracks on the principal entrance.
* Mexican Proteccion Civil has evacuated people from the beach as a precautionary measure

–  Update 17:17 UTC
* At least 60 Americans have asked their touring companies to be transferred away from their vacation location at Bahía de Kino.
* Proteccion Civil Mexico has reported that they have had NO reports of damage or injuries in Guerrero Negro.  One of the main reasons that this earthquake will have been harmless may have been the short duration of the shaking (10 seconds in Hermosilla)
– An ER reader living in Tucson, Arizona (USA) mentioned having felt the earthquake !

Strike-slip type of earthquakes

– Since the mainshock, the earthquake area has been hit by 6 aftershocks varying in strength in between M3.7 and M4.8.

– The earthquake was felt strongly. There have been 2 confirmed reports in San Luis of a VI intensity (72km from the epicenter). This means that there is the potential for VII-VIII in the epicentral area (damaging). (we are choosing to ignore a response of VII, which came 354km from the epicenter).

– Historic damaging earthquakes of similar magnitude have occurred once in the epicentral region with a M7.0 earthquake in 1954 causing no deaths and minor damage. This is a good sign for the region affected.

– Looking at the epicentral area – the location is very sparsely populated with only a few houses along the coastline apart from Santa Isabel.

– Mexican hypocenter (UNAM) is at M6.8 and 10km depth, under land.

– USGS hypocenter is at M6.9 and off the coast – there is little chance of a tsunami due to the fault mechanism.

– The area around Santa Isabel is most at risk from the USGS-based hypocenter with a possible shaking of VII. Some damage should be expected. Currently Agua de Soda and other towns closeby near the national park of Baja California are most at risk from the Mexican hypocenter which is below land.

– The Mexican Civil Defense who is responsible for Search and Rescue and first aid has reported that so far NO damage or injuries has  been recorded.

– Based on the Geofon data both earthquakes were strike-slip earthquakes (mainly lateral movement).

– The average shaking recorded in Hermosilla is MMI IV (based on 84 reports). The shaking in Guerrero Negro is MMI V (moderate).  Hermosillo is 10. km from the epicenter and Guerrero Negro 133 km. As explained before our attention goes to the immediate area of the epicenter (very shallow earthquake) – 30 to 40 km radius is at risk for eventual damage. Whether there will be damage or not will depend on how long both shakings have lasted and on the final earthquake data numbers.

– As the earthquake struck in a coastal area, NOAA has written in his latest report (for USA people mainly) : A strong earthquake has occurred, but a tsunami IS NOT expected along the California, Oregon, Washington, British Columbia, or Alaska coast. NO tsunami warning, watch or advisory is in effect for these areas. Based on the earthquake magnitude, location and historic tsunami records, a damaging tsunami IS NOT expected along the California, Oregon, Washington, British Columbia, and Alaska coasts.

– So far we have no news of the epicentral area.

– The earthquake happened just after midnight. Mexican news channels haven’t picked up the news yet.  Of course it is in the middle of the night in Mexico and people seem to have been used to the many earthquakes of the last 24 hours.

– The set of earthquakes in the Gulf of California have started with a M4.7 earthquake, followed 18 minutes later by a M6.2 earthquake and another 9 minutes later with a M6.9 earthquake (the most powerful so far)

– USGS has calculated that 3000 people will have experienced a very strong shaking and that 105,000 have experienced a strong shaking. Both these areas are at risk for eventual damage, especially because 9 minutes earlier another very strong earthquake struck the same area.

– The Mexican Servico Sismologico Nacional reports a magnitude of 6.8 with an epicenter below land. These makes this earthquake the most dangerous in 24 hours !

– Although it is a ridge earthquake, the epicenter of the M6.9 quake looks to be very close to the coast which makes this earthquake (the second very strong in a matter of 9 minutes) EXTREMELY DANGEROUS for shaking damage and fatalities. Let us hope that we are too pessimistic here. The kind of shaking will depend on the focal mechanism

– Following calculations by the USGS (providing that the earthquake data are correct) a MMI VII will have been experienced on the Baja California peninsula ! This means dangerous for the coastal areas experiencing this kind of shaking.

– The whole North American continent is currently moving in such a way that the earthquakes of the last 12 hours are somehow related (Mexico Sur, Mexico Gulf of California, Utah, Oregon) . Scientists will have a lot of work in examining eventual relationships however there is no certainty at all that a relation would exist (at least for a couple of these earthquakes)

– We are talking in this case about a Ridge earthquake, this means 2 separating plates who are hanging and suddenly get away from each other. Ridge earthquakes are typical for Middle Ocean locations

– The earthquake struck just after midnight

– We are currently collecting data

for more information and updates, go to:    http://earthquake-report.com/2012/04/12/very-strong-earthquake-in-the-gulf-of-california/