GeoLog

seismology

Shaking on Christmas Day: what we know about the 7.6 M Chile earthquake

Chile, Chiloe earthquake

While the majority of us were midway through our Christmas Day celebrations, a powerful 7.6 M earthquake struck off the western coast of the Chile. Natural hazards are not bound by time, location or festivities; an earthquake can happen at any time in any place, regardless of the significance of the day. As a result, in this earthquake prone region, raising awareness of the risk posed by natural hazards is vitally important.

The Christmas Day quake struck 42 km south west of the port city of Quellón, on the rural island of Chiloé at a depth of 34 km. Despite the powerful shaking, the tremor caused no casualties and damage to infrastructure was limited. For a time, services (such as water and power) to the southern tip of Chiloé were cut. Most affected were roads and bridges, particularly the recently renovated highway 5, which links Quellón with the fishing town of Chonchi.

The earthquake triggered a tsunami warning, leading to the evacuation of 4000 people in the coastal areas of Los Lagos Region, including the towns of Quellón and Chonchi. However, no tsunami waves were reported and the warning was lifted some 90 minutes after the temblor.

Chile’s long history of powerful earthquakes

As recently as September 2015, an 8.3 M tremor hit Illapel, causing 13 casualties, 6 missing and triggering a 4.5 m tsunami wave, with shaking felt as far as Bolivia and Argentina.

A powerful, and destructive, 8.8 M quake struck Maule in February 2010. On land, there was severe loss to infrastructure and housing, while a tsunami wave caused significant damage to coastal areas. Combined, the earthquake and tsunami resulted in the deaths of more than 500 people.

The most powerful tremor ever recorded, the estimated 9.5 M Valdivia earthquake, struck Chile in May 1960. More than 2,000 people were reported dead, a further 3,000 went missing and over 2,000,000 were left homeless. The damage in Southern Chile alone amounted to over $550 million. Tsunami waves generated by the quake struck Hawaii, Japan, the Philippines and the western USA coast, causing a further $50.5 million in damages and killing 231 people.

Damage to houses after the Valdivia earthquake, Chile

Damage to several houses in Chile after the earthquake. Credit: Pierre St. Amand – NGDC Natural Hazards Slides with Captions Header, Public Domain (distributed by Wikimedia Commons)

What causes earthquakes in Chile and what does the future hold?

Chile lies along the Pacific Ring of Fire, an area known for its high seismic and volcanic activity. Here, tectonic plates slide against each other, pull apart or converge and subduct under one another generating geologically active zones.

To understand why powerful earthquakes occur in Chile, we asked Cindy Mora Stock, a seismologist at the University of Concepción (Chile), to give us a more detailed insight into the tectonics of the region:

Earthquakes along the Chilean coast occur at the interface between the South American plate and the subducted Nazca plate. The rapid velocity between these plates (66 – 90 mm/yr) increases the potential for great earthquakes in the region, presenting on average an event of magnitude 8, or larger, every ten years. As a comparison, the Antarctic plate subducts under South American plate at a much slower rate (16 – 22 mm/yr).

The latest Mw 7.6 earthquake near Quellón on 25th of December [1], falls in the central part of the rupture zone (the portion of the fault which slipped during) of  the Valdivia earthquake – roughly 380 km south from Valdivia.

A study by Lange et al in 2007 showed a cluster of four main 4.0 < Ml < 4.4 events and their afteshocks, occurring at the interface between 12-30 km depth, beneath the western coast of Chiloe Island. Another study by Moreno et al in 2011 shows some patches at the interface that ruptured during the previous 1960 event, which are more stuck than other areas at the same interface.

Especially, computer simulations show the interface at the center part of the 1960’s rupture zone is fully locked, this means that part is “stuck”, not moving, and accumulating energy. Zones that present a high locking rate have shown to be prone areas for the nucleation of a great earthquake in the future. Although in all presented scenarios the Chiloe Island presents a high locking rate, this is not enough to state a range of time when an earthquake will occur at this patch.  Considering this, the previous seismicity, and the present Mw7.6 earthquake in the region it might seem like the interface might have ended its and it is starting to build up stress for a future earthquake.

By Laura Roberts, EGU Communications Officer, and Cindy Mora Stock, postdoctoral researcher at the University of Concepcion, Chile.

 

References and further reading

[1] Intensities of shaking felt after the 25 December earthquake (in Spanish): http://www.sismologia.cl/events/sensibles/2016/12/25-1422-28L.S201612.html

[2] Lange, D., Rietbrock, A., Haberland, E., et al.: Seismicity and geometry of the south Chilean subduction zone (41.5°S–43.5°S): Implications for controlling parameters, Geophysical Research Letters, 34, L06311, doi: 0.1029/2006GL029190, 2007

[3] Moreno, M., Melnick, D., Rosenau, M., et al.: Heterogeneous plate locking in the South–Central Chile subduction zone: Building up the next great earthquake, Earth and Planetary Research Letters, 305, 3-4, 413-424, doi: 10.1016/j.epsl.2011.03.025, 2011 (Paywalled)

USGS overview of M7.6 – 42km SW of Puerto Quellon, Chile (includes shake maps, regional tectonic information and moment tensor details): http://earthquake.usgs.gov/earthquakes/eventpage/us10007mn3#executive

Understanding Tectonic Processes Following Great Earthquakes (Eos: Earth & Space Science News)

25 December earthquake in the news:
·         Chile earthquake tsunami warning lifted (BBC News report)
·         Major quake jolts Chile tourist region on Christmas Day (Reuters in-depth news report)
·         Chile jolted by major 7.6-magnitude earthquake (Guardian News)
·         Imagenes del terremoto al sur de Chile (in Spanish: Images of the earthquake in Southern Chile – Gestión, diario de econimía y negocios de Perú)

Imaggeo on Mondays: Aoraki & a round-up of the latest New Zealand earthquake news

Imaggeo on Mondays: Aoraki & a round-up of the latest New Zealand earthquake news

On Sunday the 13th November, New Zealand’s South Island was struck by a powerful 7.8 M earthquake. Initial analysis by the United States Geological Survey (USGS) indicates that the source of the tremor was faulting on or near the boundary between the Pacific and Australia plates. A tsunami alert (no longer active) was triggered following the earthquake, with risk of tsunami waves along coastal areas. The maximum wave high recorded by a gauge at Kaikoura, 181 km north of Christchurch, was 2.5m, according to Weatherwatch.co.nz.

The collision of the two plates is also responsible for the formation of the Alpine Fault, which runs along the western flank of the Southern Alps, (Kā Tiritiri o te Moana). The mountain range runs 500km along the South Island, explains Katrina Sauer on our open access image repository, Imaggeo.  In addition, the Alpine Fault is responsible for the uplift of this impressive mountain range. Sunkissed by a setting sun (pictured above), Aoraki/Mt. Cook is the highest mountain in New Zealand (3,724 m). Katrina took the beautiful picture from Mueller Hut.

For more information about yesterday’s earthquake, as well as photographs which depict the staggering aftermath of the tremors see the list of links below (by no means exhaustive):

For some of the latest news about the earthquake, you might also follow the #eqnz  and  #nzearthquake on Twitter. For details about New Zealand geology and why and how it’s tremors are triggered, you can follow Chris Rowan  (@Allochthonous), Jascha Polet (@CPPGeophysics), @IRIS_EPO (particularly good for teaching resources for kids), and Anthony Lomax (@ALomaxNet) (among many other  great scientists!).

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Communicate Your Science Competition Winner Announced!

Congratulations to Beatriz Gaite, the winner of the Communicate Your Science Video Competition 2016. Beatriz is a researcher at the department of Earth’s Structure and Dynamics and Crystallography at the Instituto de Ciencias de la Tierra Jaume Almera (ICTJA-CSIC), in Spain.

Want to communicate your research to a wider audience and try your hand at video production? Early career scientists  who pre-registered for the 2017 EGU General Assembly are invited to take part in the EGU’s Communicate Your Science Video Competition! Find out more – importantly, when to submit your entries – about the competition!

Counting the cost of natural disasters

Counting the cost of natural disasters

Often, in the news, we are used to seeing disaster statistics reported as isolated figures, placed into context by the tragic human cost of floods, earthquakes and drought. The recent Ecuadorian earthquake that occurred on Saturday the 16th April, for example, was described as having an estimated economic cost of $820 million, which could rise as the scale of the disaster is revealed. But beyond the shocking levels of destruction that these numbers can represent, can they teach us anything of humanity’s resilience to natural disasters?

Well, according to Dr James Daniell, a civil/structural engineer and geophysicist from the Karlsruhe Institute of Technology (KIT) in Germany, by combining the data for disasters reported between 1900 and 2015, interesting trends in vulnerability across the globe are revealed. Dr Daniell, who presented his results to the European Geoscience Union this week, along with colleagues from KIT and the General Sir John Monash Foundation, Australia, has discovered that up to $7 trillion worth of economic losses have occurred globally since 1900. This value was revealed by comparing economic costs for various natural disasters including floods, earthquakes, volcanoes, storms and drought using a collection of socio-economic indicators called the CATDAT Damaging Natural Disaster database.

Of this $7 trillion, the majority of financial costs have been from flooding disasters, which accounted for just over a third of losses. Since the 1960’s, however, this trend has started to shift, with storms and storm surges accounting for 30% of the losses. Storm and flooding damages have presented an interesting challenge for Dr Daniell and his team, as it can be difficult to separate the financial costs of these similar and often connected disasters. Luckily, the database has amassed over 30,000 sources in over 90 languages to attempt to clarify the various sources of economic loss.

Deaths due to natural disasters since 1900 (Credit: James Daniell, KIT)

Deaths due to natural disasters since 1900 (Credit: James Daniell, KIT)

As well as looking at trends over the last 115 years, by examining the relationships between disasters, socio-economic losses and vulnerability, Dr Daniell has come to a surprising realisation. Although the total number of deaths in disasters appears to be increasing, in comparison with the total global population the percentage of deaths is actually in decline, and so too is the associated economic cost for society.

“Here there is a clear trend, that many (but not all) countries are protecting themselves better against disasters by building better, and therefore and are reducing their risk of high losses.”

Dr Daniell also says that his data highlights the noticeably positive impact that flood prevention infrastructure, education and communication is having on resilience to flooding.

“Over the entire time period, half of people died due to flood. However, with better planning, warnings and preventive measures, the death rate due to floods is significantly decreasing.”

An additional benefit of this database is the rapid assessment of the potential economic consequences for future natural disasters it can provide, making it easier for communities and governments to plan for large scale natural disasters. It is clear the benefits of this study and the CATDAT database will continue to assist us into the future, in our attempts to manage the risks of our planet’s most destructive forces.

By Hazel Gibson, EGU General Assembly Press Assistant and Plymouth University PhD student.

Hazel is a science communicator and PhD student researching the public understanding of the geological subsurface at Plymouth University using a blend of cognitive psychology and geology, and is one of our Press Assistants this week.