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London’s overdue killer quake: a case study in media sensationalism 17 September 2010

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Earthquakes are even less amenable than volcanic eruptions to effective forecasting. Unlike volcanoes with their precursory signals, earthquakes rarely give any warning of what is about to happen. As with volcanoes, though, what has happened in the past at a particular location can offer valuable indications of what may happen in the future, so the evidence left by the earthquakes of the past is an important source of information for the earthquake scientists, civil defence authorities and town planners of today.

Which is where historians come into the picture. Significant earthquakes in populated places rarely pass unnoticed: people write about them, study them, and publish accounts of them in all kinds of ways, creating written evidence that can be used alongside other sorts of data to inform our knowledge of earthquakes in a particular area throughout history. Gathering this information together and making it available is a big job, and for the last few years Italy’s Istituto Nazionale di Geofisica e Vulcanologia (INGV) has been leading an international project involving earth scientists and historians who have been assembling an online database of historical earthquake data. The initial result is the AHEAD database (Archive of Historical EArthquake Data – not too contrived an acronym, as these things go), which brings together data on the most significant damaging earthquakes in Europe from 1000 to 1963.

Among the INGV’s partners in this project is the British Geological Survey (BGS). To accompany the launch of the AHEAD site the BGS has an article on its website by seismologist Dr Roger Musson entitled ‘Are yesterday’s earthquakes tomorrow’s disasters?’ which explains the rationale behind the project, examines the way in which increasing urbanization makes human society more vulnerable to earthquakes, and has some interesting things to say about Britain’s earthquake history. An earthquake in the Straits of Dover in 1580 of estimated magnitude 5.5, for example, caused damage in London and south-eastern England, and two people were killed. There was a similar earthquake in the same location in 1382. Dr Musson’s article ends thus:

What has happened twice can happen a third time; what will be the effects on the London of today? In 1580, two people in London were killed. Modern London has about 40 times as many people living in it and while a comparable earthquake would certainly not cause a disaster on an international scale, the level of shaking would come as an unpleasant shock in a country that tends to think of itself as immune from earthquakes.

(more…)

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Chile: increased activity at Planchón-Peteroa 8 September 2010

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Planchón-Peteroa volcano is in central Chile, on the Chile-Argentina border. The complex history of this stratovolcano has produced the present-day nested group of three volcanoes: Azufre, Planchón and Peteroa. All historical eruptive activity has originated from Peteroa – there have been several explosive eruptions of VEI=1 and VEI=2 since the 1870s. Recent fumarolic activity in 2006, 2008 and 2010 underlines that this is very much a restless active volcano.

Reports from Chile indicate that Planchón-Peteroa’s activity is currently increasing and becoming more explosive; on 4 September an Argentine Air Force flight apparently encountered ‘a column of gas and ashes’ reaching up to two kilometres altitude, and the Air Force has also said that an area of 120 square kilometres around the volcano is being affected by ashfall. The Chilean state geological service SERNAGEOMIN issued a bulletin yesterday reporting a change in the activity of Planchón-Peteroa, from its habitual fumarolic venting to ‘eruptive activity’, albeit ‘minor up to now’:

Currently and from a technical point of view, the volcano is changing to moderately explosive eruptive activity, with a phreatic-vulcanian component (solid material) in the acid lakes of the crater zone.

Occasionally during 6 September an eruption column of pyroclasts and gases was observed, black in colour, which reached up to 1,200 metres above the crater zone, with a dispersal plume reaching at least 30 kilometres in length, mostly towards the east and, in a small percentage, to the north and south.

The bulletin notes that a ‘rock-fracturing’ earthquake of magnitude 5.2 at a depth of 13.4 kilometres was recorded on 6 September some 9 kilometres south-east of the volcanic complex. SERNAGEOMIN will be installing a seismological network and working with other Chilean agencies to maintain a full programme of monitoring at Planchón-Peteroa.

There have been suggestions that the current activity may have been sparked by the February 2010 Chilean earthquake (Erik has more on this at Eruptions), which is not the first time an earthquake has been put forward as a possible cause of eruptive activity at Planchón-Peteroa: Watt, Pyle and Mather (2009) suggest (in their Table 2) that an eruption of this volcano in July 1960 may have been triggered by the earthquake of May 1960. Watt et al argue that the incidence of volcanic eruptions in the aftermath of large earthquakes is signficant enough to justify the conclusion ‘that seismic eruption triggering following large earthquakes, with delays of several months, is a significant process in volcanic arcs’ without it being possible to pin down individual eruptions as being the result of particular earthquakes, and certainly it is not possible to say that the 2010 earthquake is responsible for the current activity at Planchón-Peteroa, any more than the same could be said for 1960. There is just not enough evidence to make a solid connection, and anyone who jumps right in with a declaration that big earthquakes = more volcanic eruptions is going way too far, but it’s an important and very interesting line of research; given the complex tectonic context of Planchón-Peteroa there is clearly much more work to be done before a clear conclusion can be reached.

[Thanks to Guillermo for pointing me to Planchón.]

References
José Cembrano & Luis Lara, ‘The link between volcanism and tectonics in the southern volcanic zone of the Chilean Andes: a review’, Tectonophysics, vol. 471, issues 1-2 (9 June 2009), pp. 96-113. [doi:10.1016/j.tecto.2009.02.038]
Daniel R. Tormey, Frederick A. Frey & Leopoldo Lopez-Escobar, ‘Geochemistry of the Active Azufre—Planchon—Peteroa Volcanic Complex, Chile (35°15′S): Evidence for Multiple Sources and Processes in a Cordilleran Arc Magmatic System’, Journal of Petrology, vol. 36, no. 2 (April 1995), pp. 265-298. [doi: 10.1093/petrology/36.2.265]
Sebastian F. L. Watt, David M. Pyle & Tamsin A. Mather, ‘The influence of great earthquakes on volcanic eruption rate along the Chilean subduction zone’, Earth and Planetary Science Letters, vol. 277, issues 3-4 (30 January 2009), pp. 399-407. [doi:10.1016/j.epsl.2008.11.005]

News
Entró en actividad el volcán Peteroa, en la frontera entre Mendoza y ChileLa Capital, 6 September 2010
Preocupa actividad de volcán PeteroaLa Estrella de Concepcion, 6 September 2010
Región del Maule: Sernageomin detecta actividad irregular en volcán Planchón y monitorea el Peteroa – Radio Bío-Bío, 7 September 2010
Planchon volcano starts spewing rocks, gases, Chile’s geology service says – Bloomberg, 7 September 2010
Volcán Planchón entró en actividad eruptiva en la Región del MauleEl Mercurio, 8 September 2010

Information
Global Volcanism Program: Planchón-Peteroa – summary information for Planchón-Peteroa (1507-04=)

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Chilean volcanoes: all quiet after the earthquake, reports SERNAGEOMIN 5 March 2010

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Villarrica volcano 5 March 2010 (OVDAS Pucon webcam)
Villarrica volcano from the Pucón webcam, 5 March 2010 (OVDAS).

In the wake of the M8.8 earthquake of 27 February, which led to speculation about the quake’s possible effects on the local volcanoes, the Chilean state geological service SERNAGEOMIN carried out an evaluation of activity at the volcanoes that are currently monitored in Chile. On 3 March a special volcanic activity bulletin was issued reporting that there is nothing unusual going on at any of the monitored Chilean volcanoes: ‘the levels and characteristics of seismic activity at Llaima, Villarrica, Chaitén, Mocho-Choshuenco, Osorno, Carrán, Calbuco and San Pedro volcanoes have shown no significant changes associated with the seismic event and activity is currently stable’. The caldera webcam at Chaitén ‘shows that the dome remains stable’, and the cameras at Llaima ‘show no significant changes in the fumarolic activity or the morphology’ of the volcano. The Villarrica webcams show ‘no major morphological change in its surface’, and visual observations of Osorno, Calbuco and Yate ‘show no abnormal situations’. (Chilean volcano webcams can be accessed via the OVDAS website.)

An overflight of Villarrica and Mocho-Choshuenco volcanoes took place on 28 February, to ‘evaluate possible changes both in activity and in glaciers and flanks’. The overflight revealed a gas and water vapour fumarole at Villarrica: this activity is described as ‘within the normal state’ of the volcano. No activity was seen at El Mocho volcano. The bulletin also notes the following observations:

The icecap on Villarrica volcano showed some new cracks and fissures on the flanks of the principal cone near the summit, caused by the 27 February earthquake, although the dimensions were smaller than those routinely present in the icecap. In addition, some small falls of ice were observed on the south flank and a small snow avalanche on the north-west flank. In the upper part of the cone of Villarrica volcano and on the north, north-west and west flanks abundant falls of rock from the summit onto the icecap and, locally, on escarpments of the flanks. In the case of Mocho volcano, small cracks were observed only on the south-east flank of the cone, the rest of the icecap showed no changes.

The OVDAS Pucón webcam shows Villarrica producing a faint fumarole this morning (see picture above).

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Chile tsunami: images of the aftermath 3 March 2010

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Dichato, Chile, February 2010 (Juan Eduardo Lopez, El Mercurio)

The Chilean newspaper El Mercurio has published a series of dramatic high-definition aerial photographs of the devastation caused along Chile’s coast by the tsunami associated with the 27 February 2010 earthquake.

Fotos aéreas del terremoto en ChileEl Mercurio, 2 March 2010

[Thanks go to Guillermo for the link.]

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Chile: big quake = more volcanic activity? 2 March 2010

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The M8.8 earthquake that hit Chile at the weekend has raised the question of whether such large quakes have any effect on activity in nearby volcanoes. In Chile itself, geologists from Chile’s Observatorio Volcanológico Andes del Sur (OVDAS) have publicly ruled out any such connection; New Scientist, by contrast, has a headline excitedly claiming ‘Volcanic explosions expected in Chile quake’s wake’.

The New Scientist article refers to a research paper by Sebastian Watt, David Pyle and Tamsin Mather of the University of Oxford which appeared in Earth and Planetary Science Letters in 2008 (‘The influence of great earthquakes on volcanic eruption rate along the Chilean subduction zone’, Earth and Planetary Science Letters, vol. 277, nos. 3-4, 30 January 2009, Pages 399-407 [doi:10.1016/j.epsl.2008.11.005]). This paper looked into a potential connection between earthquakes and increased local volcanic activity in Chile over the past two centuries, and concluded that there was some evidence of such a connection:

We show a significant increase in eruption rate following earthquakes of MW > 8, notably in 1906 and 1960, with similar occurrences further back in the record. Eruption rates are enhanced above background levels for ~ 12 months following the 1906 and 1960 earthquakes, with the onset of 3–4 eruptions estimated to have been seismically influenced in each instance.

Given the claim that the ‘enhanced’ eruption rates may manifest over around 12 months after the earthquake, OVDAS’s denial that the 27 February quake will produce an increase in volcanic activity is premature. However, the 2008 paper raises many questions about the nature of the mechanisms at work, the time lag involved, and the real significance of the phenomenon (an estimated 3-4 additional eruptions is not very many). As Erik Klemetti has just observed,

Complex systems have many inputs – maybe the volcano that erupts next week would have erupted with a magnitude 4 earthquake, maybe it would have erupted without an earthquake at all. To connect the two merely because they are temporally juxtaposed is not scientifically sound. There is evidence that there could be an effect on nearby volcanism after large earthquakes in some settings, however, it is far from proven.

A further point is that, whatever New Scientist‘s headline writer may think, not all volcanic activity is explosive, or even dangerous in any way. Increased volcanic activity does not necessarily equate to increased hazard – as David Pyle points out in the New Scientist article: ‘At volcanoes that are already active we might see an increase in steam explosions, but we don’t expect it to present a significantly increased danger’. So even if there is a volcano-earthquake connection, and the question very much remains open, it is not necessarily something people living in active subduction zones should consider an additional significant threat.

N.B. ‘Llaima, one of the largest and most active volcanoes in Chile, is back on the watch list’, says the caption to a dramatic picture of Llaima accompanying the New Scientist story. In fact Llaima has been ‘on the watch list’ (if that means ‘at higher alert’) since mid-February, but of course it increases the drama to imply that the raised alert level is the result of the earthquake, and if that misleads your readers, so what?

News
Descartan que volcanes Llaima y Villarrica estén con actividad irregular luego de terremotoLa Tercera, 28 February 2010
Descartan que el terremoto un aumento de la actividad volcánica – Europa Press, 1 March 2010
Completa normalidad se observa en volcanes de la zonaEl Austral, 1 March 2010
Volcanic explosions expected in Chile quake’s wakeNew Scientist, 1 March 2010

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Magnitude 8.8 earthquake in Chile 27 February 2010

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A large earthquake has taken place off the coast of Chile. The quake occurred at 03:34 am local time (06:34 GMT) today. The USGS initially reported a magnitude of 8.3, but that has just been upgraded to 8.8. The earthquake was located off Maule, 325 km SW of the capital Santiago and 115 km NNE of the city of Concepción, with a reported depth of 35 km. The NOAA Pacific Tsunami Warning Center (home page) reports that a tsunami warning has been issued for Chile and Peru, and a tsunami watch has been issued for Ecuador, Colombia, Antarctica, Panama and Costa Rica. The BBC reports that the Japan Meteorological Agency ‘has warned of a potential tsunami across the Pacific’ (NOAA tsunami travel time map).

Little news is available from Chile at the time of posting (it is less than two hours since the earthquake). La Tercera is reporting at least two deaths, power cuts, damage to communications networks and extensive property damage. UPDATE: Reuters, quoting Chilean President Michele Bachelet, reports that ‘at least six people’ have been killed.

FURTHER UPDATE: The confirmed death toll has risen to 47, and a state of emergency has been declared in the most seriously affected regions of central Chile. Chilean television station 24 Horas is now (11:31 GMT) reporting 64 dead. Live streaming of Chilean television (24 Horas) here.

[The Volcanism Blog will be back on Monday.]

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Iceland’s Reykjanes Ridge a-rumbling 18 February 2010

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Earthquake activity in south-west Iceland, 18 February 2010 14:35 UTC (Iceland Meteorological Office map)

Back in November 2009 we reported (thanks to Boris Behncke) that there was significant earthquake activity along the Reykjanes Ridge south-west of Iceland. Well, it seems to be happening again (and again, thanks to Boris for the tip-off). The above detail of the earthquake activity map at the Iceland Meteorological Office website shows the recorded quakes up to 14:35 UTC today; the largest quakes have been between magnitudes 3 and 4. This is a volcanically-active area (part of the Mid-Atlantic Ridge System) and it’s worth keeping an eye on what happens there.

UPDATE 19 February 2010. Erik has posted a very informative piece on the Reykjanes Ridge quakes at Eruptions.

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Japan: Kurikoma activity raises questions 17 June 2008

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Hot gas plumes thought to consist of volcanic gases have been detected 7km south-west of the summit of Mt Kurikoma, a 1628m stratovolcano in northern Honshu (see Erik’s Eruptions blog for more). Kurikoma last erupted in 1950, and has in general a rather sketchy eruptive history.

The volcano is in the area affected by Friday’s 6.8M earthquake, so are these phenomena related? Here’s what the Japanese press report says:

Associate Prof. Sadato Ueki of Tohoku University’s Research Center for the Prediction of Earthquakes and Volcanic Eruptions said the plumes might be volcanic gases rising to the Earth’s surface.

‘There’s a possibility that volcanic gases that had been confined below ground are gushing out through fissures in the mountain created by the earthquake,’ he said.

Ueki said it was also possible that the plumes were steam coming from underground hot water channels that had their course diverted by the earthquake.

But the professor ruled out the possibility of increased volcanic activity on Mt. Kurikoma, saying that the plumes were very far from the summit of the volcano.

So the professor is suggesting the plumes might be by-products of the earthquake. Kim at All of My Faults Are Stress-Related similarly asks ‘Did the earthquake … cause Kurikoma to start acting up?’, but also observes that this was a rather unusual earthquake. It was along a thrust fault, but it was in Honshu’s volcanic arc, which is not where you would expect a thrust earthquake to be. Kim asks whether the quake itself might be the result of local magmatism: ‘the fault mechanism isn’t surprising. But the location is. Is this a case where the magmatism created a weaker zone in the crust and allowed thrust faulting to take place?’

It will be interesting to watch what happens.

Information
Global Volcanism Program: Kurikoma – summary information for Kurikoma (0803-21=)

News
Hot gas plumes detected at Mt. KurikomaDaily Yomiuri Online, 17 June 2008

The Volcanism Blog

The Daily Volcano Quote: earthquakes and volcanoes – the view from 1930 6 June 2008

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For many years earthquakes and volcanoes were closely associated in the public mind. We now know that, while they are related, and all volcanic outbreaks are accompanied by earthquakes, all the greater earthquakes occur in regions remote from volcanoes or if in volcanic regions at a time when the volcanoes are not active. In the great Japanese earthquake of 1923 Fujiyama, an extinct volcano, was strongly shaken but was not roused to activity. On the other hand, the greatest eruption of Vesuvius in recent times was an explosive outburst near the same time as the California earthquake of April, 1906. This may have been a coincidence, but there may have been some relation, though if so it was more probably in the trigger force which timed the events than the events themselves. It would seem that the volcano is a localized and rather superficial phenomenon as compared to the earthquake.

N. H. Heck, ‘Earthquakes, a challenge to science’, The Scientific Monthly, vol. 31, no. 2 (August 1930), pp. 113-125, here p. 116.

The Daily Volcano Quote: from Monday to Friday, a new eruption of volcanic verbiage each day.

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