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Seismic swarm at San Salvador volcano alarms authorities

Authorities today ruled El Salvador declare an emergency for low-magnitude earthquakes that have shaken the Salvadoran capital, all centered in the San Salvador volcano, eight of them felt by the population and the strongest of 3.3 degrees on the Richter scale.

“There is no evidence that we are facing a potential emergency,” said Minister of Environment and Natural Resources, Herman Rosa Chavez, in a press conference in which he reiterated that no volcanic tremor, but tectonic.

“We did analysis of temperature in the area and there is no evidence that this is associated with volcanic activity, this has to do with the activation of local faults, which is something that happens and has happened before,” he said.

The eight tremors felt by the population have reached levels of between 2.2 and 3.3 degrees on the Richter scale, according to the National Service of Territorial Studies (SNET), which has recorded at least 25 microearthquakes.

The first quake was felt that reached 2.6 degrees and was registered at 01.22 local time (7.22 GMT), and most recently, of 2.7 degrees, at 15.50 (21.50 GMT).

The strongest earthquake of 3.3 degrees, occurred at 08.01 (14.01 GMT), said the SNET.

He added that the focal depth of earthquakes has fluctuated between 0.5 and 5.8 kilometers, so they felt in various parts of the city, near which is the San Salvador volcano, which is inactive.

Likewise, the eight earthquakes have reached an intensity of two on the Mercalli scale, whose maximum is 12, in San Salvador.

The Ministry of Environment and Natural Resources in a statement recalled that the last seismic swarm with epicenter in the San Salvador volcano was in 2007 when there were 142 microearthquakes, four of them felt by the population.

Apart from the string of earthquakes in San Salvador, today reported another quake Snet of 4.3 on the Richter scale at 11.26 local time (17.26 GMT) in Pacific Ocean, about 43 kilometers south of the estuary San Diego, in the department of La Libertad (center).

…(Univision)

March 23, 2012 Posted by | Seismic, Violence | , , , , , , , , | Leave a comment

Volcanologists Monitor Swarm of New Tremors at El Hierro

The submarine eruption south of El Hierro Island could be in a process of change: While visible activity on the sea surface above the vent, as well as harmonic tremor signal (thought to be more or less proportional to erupting magma flux) have nearly ceased, the number of earthquakes under the island has increased sharply since yesterday.

On 15 February, more than 20 quakes were measured. Most of the earthquakes were very small, well below magnitude 2, and were clustered beneath the NW and SW sectors of the island at depths of around 10 km. There is no conclusive interpretation of this measurement.

A possible (and usually assumed) scenario is that rising new magma from the mantle reservoir is creating new intrusions and rupturing rock to create pathways in the crust under El Hierro, not using the same paths as until now. That would explain why less magma is currently being erupted at the current vent(s). In that scenario, the eruption will continue, perhaps even from a different vent, and an increase in magma output is going to be expected any time soon. However, this is speculation.

The earthquakes could as well be related to some other (known or unknown) process, e.g. gravity-induced adjustments that respond to pressure changes and occur within previously ruptured areas of the crust beneath the island.

The next days or weeks will show what happens next.

…(Volcano Discovery)

February 17, 2012 Posted by | Science, Volcanic | , , , , , , | 1 Comment