Mexico quake data show 'very strong' shaking

The USGS Earthquake information Center offers data about Monday morning's earthquake that quantifies the expected level of damage and loss of life.

Posted 1:52 p.m. Jul 7, 2014 — Updated 2:07 p.m. Jul 7, 2014

Mike Moss

About 7:24 a.m. Monday, an earthquake currently estimated to have a magnitude of 6.9 struck just inland of the Pacific coast of Mexico a short distance from the city of Puerto Madero, which is about 20 miles from the border with Guatemala.

We've started to receive some initial reports of fatalities from the region, and, based on automated estimates from the USGS Earthquake information Center, unfortunately it is quite possible the numbers will climb as new information becomes available.

The USGS site includes a ShakeMap section that estimates the intensity of shaking induced by the quake, which in this case was centered about 34 miles below sea level. The map indicates level VII shaking, which is considered "very strong," along a stretch of the Mexican and Guatemalan coasts. This level of shaking typically produces moderate damage levels, but rates moderate to severe for vulnerable structures.

Additional automated analysis on the USGS site is shown in a section labeled PAGER (Prompt Assessment of Global Earthquakes for Response), and uses geographic information system data to assess the population potentially affected by various intensities of shaking, and to roughly gauge the potential number of fatalities and economic losses, based on the expected mix of vulnerable and earthquake-resistant structures in the affected region.

In the case of the current quake, the system estimates that the most likely number of fatalities is between 10 and 100. As you can see in the second included image, however, that likelihood is only a little greater than the chance that the number is between 100 and 1,000.

Not shown here, but indicated on the PAGER site, is that a population of a little more than 270,000 people may have been exposed to the level VII shaking, and that the region contains a mix of resistant and vulnerable construction types, with most vulnerable structures either mud-walled or constructed of concrete and cinder blocks.

The web site also includes an icon that links to Tsunami Warning Centers, but so far it appears there was no significant tsunami generated by this quake. It isn't clear as yet whether that is due to the slightly inland position of the quake origination point, or because the movement associated with the quake was principally lateral rather than vertical.

I've included a link to the event overview page for those who would like to see more details or check for updates. You'll see links across the top of that page for the PAGER, ShakeMap, "Did You Feel It?," and Tsunami Warning Center sites.

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