Guest Blog: Earthquake threat to Mexico City from the Guerrero seismic gap

David BekaertDavid Bekaert is a PhD student based in the School of Earth and Environment at the University of Leeds. David’s research involves using space based remote sensing technologies to study ground motions from slow-slip earthquakes, particularly in Mexico. In today’s guest blog he relates this morning’s earthquake to the broader seismic threat faced by Mexico City.

The earth’s crust is segmented into different tectonic plates. Often large earthquakes occur on the plate boundaries where two plates move against each other. As plates do not move everywhere at the same velocity, some regions are stressed much more than others, i.e. build up more energy. This stress is released by deformation in the crust and earthquakes. The occurrence of earthquakes depends on many parameters like friction, temperature, seismic history, and many more, and for this reason cannot be predicted.

The tetconic setting for the  Guerrero seismic gap.   Image source Twitter: @AlessAmato

Figure 1: The tectonic setting for the Guerrero seismic gap.
Image source: Twitter – @AlessAmato (modified from Vladimir Kostoglodov)

In southern Mexico the heavier oceanic Cocos plate dives beneath the lighter continental North America plate with a velocity between 5.6-6.1 cm/year [1], Figure 1. This is much higher than average plate velocities. On average plates move as fast as your fingernails grow, about 3.7 cm/year [2]. In 1985, central Mexico (Michoacan) was struck by a magnitude 8 earthquake, killing 9500 people and causing 3-4 billion U.S. dollars worth of damage [3]. After this, a lot of effort was put into designing new building regulations and preparation for future earthquakes.

Today a 7.2 magnitude earthquake (USGS) occurred at 9:27 am (local time) in Guerrero, a state in Southern Mexico, about 120 km west of the coastal city of Acapulco. Initial reports indicate some damages to buildings, electric infrastructure, and roads (Figure 2), but so far no casualties have been reported by media [4,5]. This morning’s earthquake occurred in a region where no earthquake has occurred since 1911, a so-called “seismic gap”. Scientists have estimated that an earthquake of magnitude 8.0-8.4 is needed in order to rupture (remove all stresses in) this seismic gap [6]. And since the earthquake moment magnitude scale is logarithmic this requires an earthquake about 31 times stronger than the earthquake today.

Damage to road after the recent earthquake in Mexico. Image source : Twitter - @2079_carlos

Figure 2: Damage to a road after the recent earthquake in Mexico.
Image source : Twitter – @2079_carlos

The question is, whether this gap is fully loaded. Something special about the Guerrero gap is the occurrence of a new type of earthquake, which does not shake the Earth, referred to as slow slip events. In Guerrero, they have been observed using GPS about every 4-years, with the most recent event in 2009/2010. A new event is thus due soon. Unlike a regular earthquake that happens instantaneously, slow slip events last for days to months, or even up to a year, as is the case in southern Mexico. This steady sliding removes a lot of stress. In Guerrero, if you would release a slow slip event instantaneously, it would achieve an earthquake-like magnitude up to 7.4, a similar size to today’s earthquake!

While these slow slip events are not dangerous in themselves, they release energy and can change the stresses in the area, which potentially could trigger a devastating earthquake. The earthquake today occurred on the western extend of the Guerrero gap. The question for Mexico remains, how much energy have these slow slip events released in this seismic gap, enough such that no earthquake would occur?

 

References:

[1] http://geoscience.wisc.edu/~chuck/MORVEL/motionframe_mrvl.html
[2]  http://www.jclahr.com/science/earth_science/thumbnail/index.html
[3] http://earthquake.usgs.gov/earthquakes/world/events/1985_09_19.php
[4] http://edition.cnn.com/2014/04/18/world/americas/mexico-earthquake
[5] http://www.bbc.co.uk/news/world-latin-america-27081799
[6] Singh, S. K., and F. Mortera (1991), Source Time Functions of Large Mexican Subduction Earthquakes, Morphology of the Benioff Zone, Age of the Plate, and Their Tectonic Implications, J. Geophys. Res., 96 (B13), 21,487–21,502.

Video

Adapting to a Changing Climate in South Africa

This short film captures the key messages and debates emerging from the first Southern Africa Adaptation Colloquium, held in November 2013.

The film was produced to make available the discussions to audiences that weren’t able to attend the Colloquium — particularly people working with local government in African cities.

 

Image

New Radar Satellite Launch Starts New Era of Earth Observation

New Radar Satellite Launch Starts New Era of Earth Observation

A few academics from the department were invited to mission control in Germany to watch the launch of the first of a suite of earth observation satellites as part of the European Space Agency‘s flagship Copernicus program. Sentinel-1a, launched yesterday, will be the first dedicated satellite to produce around-the-clock radar images of the whole world. CGS academics,

Tim Wright and co-workers will use these images to produce high resolution maps of ground movement around the world’s hazardous tectonics belts. The Sentinel satellites will provide the most accurate and detailed ‘health-check’ for our planet including its biomass, air quality, sea level changes, natural hazards, temperature and other key features.

Ekbal

More information:
[1] http://www.esa.int/Our_Activities/Observing_the_Earth
[2] http://comet.nerc.ac.uk/current_research_look_inside.html

Climate Change will Affect People, the Environment and Wildlife

 

 

The new IPCC Working Group 2 report, released today, says that climate change is real, it’s happening now and it’s affecting the lives and the livelihoods of people, as well as the planet. According to the report, climate change has already affected agriculture, human health, ecosystems on land and in the oceans and in our water supplies. These effects are global regardless of the wealth of a nation, its size or geographical location.

The report concludes that responding to climate change involves making choices about risks in a changing world.The nature of the risks of climate change is increasingly clear. The report identifies vulnerable people, industries, and ecosystems around the world. It finds that risk from a changing climate comes from vulnerability (lack of preparedness) and exposure (people or assets in harm’s way) overlapping with hazards (triggering climate events or trends). Each of these three components can be a target for smart actions to decrease risk.

Read more about the new IPCC report at: www.ipcc.ch

The Summary for Policy Makers can be downloaded here: http://ipcc-wg2.gov/AR5/images/uploads/IPCC_WG2AR5_SPM_Approved.pdf

Read more about the IPCC report from RealClimate at: www.realclimate.org/index.php/archives/2014/03/ipcc-wg2-report-now-out

Video

IPCC Working Group 2: Impacts, Adaptation and Vulnerability

The IPCC Working Group 2 meeting is being held in Yokohama, Japan. This report will form the second part of the IPCC AR5 analysis of our current understanding of climate change.

This working group report will set out the impact that rising temperatures will have on humans, animals and ecosystems over the next century.

You can follow tweets from the meeting on #AR5.

Ekbal

Image

The World Has More Corrupt Countries Than Not

World Has More Corrupt Countries Than Not

Two thirds of the world’s countries are more corrupt than not.

Transparency International is an international movement aiming to increase transparency, highlight and tackle global corruption. Since 1993 they have published annual reports on the level of international corruption. The figure above is a screenshot image of an interactive map of the world showing global corruption perception index.

The 2013 results show that on a scale where 0 = completely corrupt and 100 = no corruption; two thirds of the world’s countries score below 50!

No country has a perfect score however Denmark and new Zealand came joint top with a score of 91 making them the least corrupt countries in the world. The lowest place (most corrupt nations) was shared by Afghanistan, North Korea and Somalia with a score of 8.

With a score of 76 the United Kingdom is 14th on the list of 177 nations and territories covered.

Ekbal

More information:
[1] http://www.transparency.org
[2] http://cpi.transparency.org/cpi2013/results
[3] http://blogs.egu.eu/gfgd/2014/01/27/guest-blog-death-by-corruption

Image

A Magnitude 4.1 Earthquake Recorded in the Bristol Channel

A Magnitude 4.1 Earthquake Recorded in the Bristol Channel

The British Geological Survey (BGS) has confirmed the recording of a magnitude 4.1 earthquake in the Bristol Channel at 13:21 on Tuesday 20th February.

Ground shaking from the earthquake was widely felt in north Devon and south Wales. Little damage is expected from an event of this magnitude and now injuries have yet been reported.

It is not unknown for parts of the British Isles to experience small to moderate size earthquakes. These are due to the sudden release of built-up stress on old fractures and faults in the ground.

The image above shows the seismograph recording of the the earthquake on the Hartland (HTL) seismic station.

A summary of the event is given below

Date 20/02/2014
Origin Time 13:21:30.1 UTC
Location 51.361 -4.184
Depth 5 km
Magnitude 4.1
Locality Bristol Channel

Picture credit: BGS

Ekbal

More information:
[1] http://earthquakes.bgs.ac.uk/earthquakes/recent_events/20140220132017.html#page=summary