# 5547
(Credit USGS)
A little over a month ago in Divining Japan’s Seismic Future I wrote about an article that appeared in the April 9th edition of the International Business Times, called:
Japan warns of massive earthquake and volcanic explosion after the April 7 earthquake
You can follow the link and read the (short) article, but the gist of the story is that the massive March 11th earthquake and subsequent aftershocks may have increased the stress on adjacent fault lines and nearby volcanoes, increasing the risks of additional seismic events including volcanic eruptions.
The idea that a large earthquake in one part of the world might trigger additional earthquakes (or volcanic eruptions) someplace far away – days, weeks, or even months later - is a controversial one.
Can a large earthquake put new stresses on distant (or even adjacent) fault lines, setting them up to fracture sooner rather than later?
In doing some research on the matter last month, I found the USGS in their FAQ About Relationships Between Earthquakes and Volcanic Eruptions - Is there a relationship between earthquakes larger than magnitude 6 that occur along major fault zones and nearby volcanic eruptions? stated, in part:
After large earthquakes the question of whether such strong events can trigger nearby volcanic eruptions often comes up. The short answer to this question is: “not very often.”
There are a few examples in the historical record that suggest a connection between large earthquakes and volcanic eruptions, but even these, on close inspection, do not show a simple causative relationship
This FAQ goes on to provide some examples of possible seismic events that may have been triggered by large nearby earthquakes. So while saying it doesn’t happen often, this FAQ isn’t completely dismissive of notion of large earthquakes acting as volcanic triggers.
In Volcanic activity before and after large tectonic earthquakes: Observations and statistical significance Silke Eggert and Thomas R. Walter provide a litany suspected seismic trigger events, including:
A well-known sequence occurred in South America wherein the volcanoes Cordón Caulle and Puyehue erupted in Chile just one day after the large 1960 Valdivia earthquake (Barrientos, 1994; Lara et al., 2004).
Other prominent examples of volcanoes that have been active in association with major tectonic earthquakes are Mount Vesuvius and Mount Etna in Italy (Sharp et al., 1981).
Fast forward a month and in a somewhat related story, yesterday the USGS posted a press release regarding a study that appears this week in Nature Geoscience.
Triggered creep as a possible mechanism for delayed dynamic triggering of tremor and earthquakes
David R. Shelly, Zhigang Peng, David P. Hill & Chastity Aiken
Here, as the press release explains, scientists looked at the effects of distant earthquakes (as small as 5.4 magnitude) on the San Andreas fault in California.
They found that even moderate seismic waves passing through the fault line can induce delayed tremors that may persist for days. Tremors they believe signify slow-motion fault slippage, that could potentially alter the timing of the next quake on that fault.
This from the USGS Newsroom.
Distant Earthquakes Can Trigger Deep Slow Fault Slip
Released: 5/9/2011 5:12:12 PMContact Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communication
119 National Center
Reston, VA 20192
Leslie Gordon
Phone: 650-793-1534MENLO PARK, Calif. — Researchers examining the San Andreas Fault in central California have found evidence that distant earthquakes can trigger episodes of accelerated (but still very slow) slip motion, deep on the fault.
While a sudden slip on a fault generates earthquakes capable of strong shaking, a fault can also slip slowly. Sometimes, these slow movements on a fault, known as creep events, are accompanied by a weak ground vibration known as a tectonic tremor, which can be detected on sensitive seismometers.
Using data from these seismometers, researchers from the U.S. Geological Survey and Georgia Institute of Technology examined the locations and timing of tremor activity following large distant earthquakes. In some cases, they found evidence that triggered slip and its associated tremor migrated along the length of the fault, and persisted long after the passage of seismic waves from the distant earthquake. The scientists hypothesize that distant earthquakes can act as a trigger for ongoing episodic creep events, sometimes altering their timing.
The researchers also noted that creep events in other locations can sometimes trigger earthquakes. While they caution that their study was focused on triggered tremor rather than triggered earthquakes, they suggest that prolonged triggered creep episodes could be relevant for both phenomena. In particular, triggered creep episodes could provide a physical explanation for the time delay commonly observed between passing seismic waves and distantly generated earthquakes.
Published online this week in the journal, “Nature Geoscience,” the study, “Triggered creep as a possible mechanism for delayed dynamic triggering of tremor and earthquakes,” is the latest of ongoing research on the effects of large earthquakes on distant faults.
While distantly triggered small earthquakes are relatively common, another recent study found no evidence for distantly triggered large earthquakes, at least during the first few days after a large event. The current study provides a possible mechanism to explain a range of time delays between a large distant event and triggered earthquakes.
The `money quote’ here appears to be near the end, which I’ve bolded.
While a large earthquake in Japan or Indonesia may not trigger contemporaneous large earthquakes elsewhere in the world, the evidence suggests that they may have a long-term delayed effect on distant fault lines.
Last month, in UNDP: Supercities At Seismic Risk, I wrote about a study that claimed that half of the world’s supercities (pop. 2-15 million) were located in high seismic regions.
Which makes research like this - that increases our understanding of the dangers of future earthquakes - not only interesting, but vitally important as well.
