Michael Linder

Seismologists at UC Berkeley say gravitational fields of the sun and moon, tugging on the San Andreas Fault, are stressing out planet Earth, triggering deep tremors that can result in earthquakes.

In a study published December 24 in Nature, Amanda Thomas, Robert Nadeau and Roland Bürgmann of the Berkeley Seismological Laboratory shed new light on geological forces churning 10-25 miles beneath Earth’s surface where the same planetary pull that raises ocean tides worldwide may also be dishing out earthquakes.

Earthquake zones lie relatively close to the surface. Look deeper, say the scientists, pointing down toward Earth’s upper mantle where enormous pressure squeezes rock into something like Silly Putty — the sun and moon’s gravities tugging on this taffyesque earthstuff.

Water or magma trapped nearby under extreme pressure may lube up this squishy rock as it squirms around during tremor spasms, weakening or loading stress on the fault zone upstairs. The effect is even more pronounced when a fault line breaks perpendicularly to tidal forces, as does California’s San Andreas.

Tidal tugging doesn’t seem to directly cause surface quakes, but its effect on tremors rumbling in deeper geology is becoming apparent along the San Andreas fault and the Cascadia subduction zone in the Pacific Northwest where volcanoes are not active, blurring mantle tremor data.

Geologists are discovering that tremors can reverberate across vast distances as low-impact, slow-motion earthquakes that rarely peak above 1 on the Richter scale.

Still, they throw around enormous energy — all over the globe. Last year’s 6.9 Sumatra earthquake touched off deep tremors an ocean away off Washington state while in 2002, California’s underpinnings echoed the impact of Alaska’s magnitude 7.9 Denali quake.

Despite their stealthiness, deep “silent earthquake” tremors may play a serious role in massive magnitude 8+ quakes that snap within a couple of miles of the surface.

Geology is discovering how to peer ever deeper, getting a glimpse of yet another set of gears inside our galactic egg — fundamental forces that may have a lot to say about what goes on up on top. Here on Earth’s crispy crust.

More at ScienceDaily.

Eye on Earthquakes:
An app for that, too

Earthquake aficionados are applauding QuakeWatch from LateNightProjects, a wonderfully elegant way to capture and display near-real time quake data from the U.S. Geological Survey. This 99¢ iPhone app does for geology what Doppler radar apps do for storm cells — displaying the power and position of every quake of 1.0 magnitude or bigger, all over the world, over the past week.

QuakeWatch plots earthquake epicenters on Google’s terrain or geopolitical maps, allowing a quake chaser to pan and zoom in on surface features or city grids that lie above an event. Each temblor’s local time, longitude, latitude, magnitude and depth are displayed in clean, concise graphics — a challenge, what with earthquakes being, like, invisible.

Tapping the QuakeWatch world map icon releases a flurry of quake map pins defining recent rumblings along tectonic boundaries and active faults — eye-opening proof of how rumble prone our planet is. Tap a pin, supporting data appears.

Thousands of sensors worldwide provide listings for the biggest or most recent quakes, sorted by magnitude or proximity to two user-defined locations along with easy access to tsunami advisories.

In text mode, quakes are color coded by intensity. Quake data can be quickly emailed, along with interactive maps. Only fault line overlays are missing, a feature developer Terence Worley is pursuing.

Still, there’s an awful lot of bang for one buck in QuakeWatch for amateur or professional geofreaks. Just don’t be thrown by how creaky supposedly solid ground truly is.

Rock on.

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One Response to...
Earthquakes: New theories, cool tools

1. Terence Worley wrote on January 2nd, 2010 at 4:26 pm

   Thanks for the spotlight Michael! I wrote QuakeWatch ’cause I wanted to keep up on SoCal quakes and am glad to see others finding it useful. One important note, be sure to turn off the EMSC (European) quake feed in the QuakeWatch settings, it is currently down and causing a delay when launching the app. Hopefully they will have it fixed soon.

   
   
   

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