GeoLog

earthquake-induced geohazards

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)

Geosciences Column: An international effort to understand the hazard risk posed by Nepal’s 2015 Gorkha earthquake

Geosciences Column: An international effort to understand the hazard risk posed by Nepal’s 2015 Gorkha earthquake

Nine months ago the ground in Nepal shook, and it shook hard: on April 25th 2015 the M7.8 Gorkha earthquake struck and was followed by some 250 aftershocks, five of which were greater than M 6.0. The devastation left behind in the aftermath of such an event, and how to coordinate disaster-relief efforts in a vast, mountainous region, is difficult to imagine. Yet, this December at the 2015 AGU Fall Meeting, I came a little closer.

At the meeting I attended the press conference ‘Future Himalayan seismic hazards: Insights from earthquakes in Nepal’. It focused, mainly, on the outcomes of two research papers published in Science on the role that both past and the recent Gorkha earthquakes can play in triggering quake-induce landslides. The findings of the research were covered widely by the media.

I was struck, not only by those findings, but by the personal accounts of the scientists who’d seen the devastation left behind by the earthquake. But more still, what really caught my attention, was the multinational effort and collaboration that went into the research.

Before-and-after photographs of Nepal’s Langtang Valley showing the near-complete destruction of Langtang village due to a massive landslide caused by the 2015 Gorkha earthquake. Photos from 2012 (pre-quake) and 2015 (post-quake) by David Breashears/GlacierWorks. Distributed via NASA Goddard on Flickr.

Before-and-after photographs of Nepal’s Langtang Valley showing the near-complete destruction of Langtang village due to a massive landslide caused by the 2015 Gorkha earthquake. Photos from 2012 (pre-quake) and 2015 (post-quake) by David Breashears/GlacierWorks. Distributed via
NASA Goddard on Flickr. Click to enlarge.

After the press conference I met with Dalia Kirschbaum of the NASA Goddard Space Flight Centre and Dan Shugar of the University of Washington Tacoma, two of the co-authors of the 2015 Gorkha earthquake paper, to discuss this aspect of the research in more detail.

Given the vast geographical area over which the Gorkha earthquake had caused damage, as well as the hard-to-access mountainous terrain, the team used satellite imagery to map earthquake-induced landslides. They also monitored the stability of the region’s moraine dammed glacial lakes, prone to outburst following earthquakes due to the failure of moraine damns.

When a large scale disaster occurs the International Charter on Space and Major Disasters allows for the dedicated collection of space data to contribute towards humanitarian and charitable efforts in areas affected by natural or man-made disasters. Following the Gorkha earthquake, Nepal called for the activation of the charter.

Following Nepal activating the Charter, satellite imagery was provided by NASA, the Japan Aerospace Exploration Agency, the China Space Agency, as well as private organisations such as DigitalGlobe, to name but a few.

This project was “different to what we had seen in the past in terms of international collaboration,” Dalia told me during our conversation.

A group of nine nations, coordinated by the Global Land Ice Measurements from Space, began assessing the imagery provided and mapping the earthquake-induced geohazards, including landslides. In the first instance the data was used to identify potentially hazardous situations where communities and infrastructure might be at risk. This was followed by an effort to build a landslide inventory, which could provide information about the distribution, character, geomorphological, lithological and tectonic controls which govern the occurrence of earthquake triggered landslides.

An international volunteer geohazards team mapped landslides triggered by the 2015 Nepal Gorkha earthquake and its aftershocks. The landslides were mapped using a range of different satellite products. Credit: Landslide mapping team/NASA-GSFC. Distributed via NASA Goddard on Flickr.

An international volunteer geohazards team mapped landslides triggered by the 2015 Nepal Gorkha earthquake and its aftershocks. The landslides were mapped using a range of different satellite products. Credit: Landslide mapping team/NASA-GSFC. Distributed via NASA Goddard on Flickr.

Simultaneously, scientists from the British Geological Survey and Durham University also began to build a database of known geohazards in the region. The data was shared between the two working groups.

“For no other major earthquakes have landslide inventories come from such a diverse range of datasets and organisations,” explained Dalia.

Neither had emergency remote sensing been undertaken so quickly.

I was interested in why the Nepal earthquakes in particular had inspired this, so far unique – but hopefully not the last – diverse international collaboration to better understand earthquake-induced geohazards.

Dan Shugar thinks it was because so many geoscientists have a deep personal connection with Nepal. Durham University scientists, for example, take geology students to the region on an annual field trip.

“Everybody loves Nepal! The nature of the country really lent itself to people wanting to help,” he added.

Field visit identifies light damage at Tsho (lake) Rolpa. Post-earthquake image of Tsho Rolpa appears identical to its appearance shortly before the earthquake. Two areas of fractures —believed formed by the May 12 2015 aftershock— were observed on the engineered part of the end moraine from a helicopter during an inspection undertaken by the U.S. Geological Survey at Tsho Rolpa. Photos from 27 May by Brian Collins/USGS, courtesy of USAID-OFDA (Office of Foreign Disaster Aid). Distributed via NASA Goddard on Flickr.

Field visit identifies light damage at Tsho (lake) Rolpa. Post-earthquake image of Tsho Rolpa appears identical to its appearance shortly before the earthquake. Two areas of fractures —believed formed by the May 12 2015 aftershock— were observed on the engineered part of the end moraine from a helicopter during an inspection undertaken by the U.S. Geological Survey at Tsho Rolpa. Photos from 27 May by Brian Collins/USGS, courtesy of USAID-OFDA (Office of Foreign Disaster Aid). Distributed via
NASA Goddard on Flickr.

For many, including Dan, it rose from a need to contribute to the humanitarian effort. Despite having trained as a geomorphologist and actively researching Alpine natural hazards, prior to the Gorkha earthquake he’d not had the opportunity to apply his knowledge and expertise to help others. It allowed him to offer help in the same way a medic might do by flying out to the scene of a disaster and offering medical expertise and treating the injured.

For Dalia, the positive impact made in the Nepal crisis by the international effort of quickly gathering, sharing and interpreting Earth observation data, was an important driver in keeping her linked to the project.

This effort is now seeing a life beyond the Nepal earthquakes. NASA satellites had previously been involved in the acquisition of data sets to aid in humanitarian crisis, such as in the aftermath of hurricanes. The successful approach taken during the Nepal earthquakes will now help coalesce NASA’s disaster programme and how NASA will respond to natural hazards in the future. It is leading to a more formalised disaster response programme.

The lessons learnt from the Nepal earthquake are ongoing, with much still being done in the scientific realms to better understand the hazards posed by the tectonics of the region, and associated geohazards triggered by the earthquakes. Many of the international collaborations fostered during the crisis are ongoing and will hopefully mean an improved response to future natural hazards in the region.

By Laura Roberts Artal, EGU Communications Officer. With many thanks to Dalia Kirschbaum and Dan Shugar.

References

Schwanghart, W., Bernhart, A., Stolle, A., et. al.,: Repeated catastrophic valley infill following medieval earthquakes in the Nepal Himalaya, Science, vol. 351, 6269, 147-150, doi: 10.1126/science.aac9865, 2016.

Kargel, J. S., Leonard, G. J., Shugar, D.H., et al.,: Geomorphic and geologic controls of geohazards induced by Nepal’s 2015 Gorkha earthquake, Science,vol. 351, 6269, 147-150, doi: 10.1126/science.aac8353, 2016.

Unfortunately, some of the publications referenced in this post are close access – but other links included in this post, as well as the post itself, hopefully convey the overall message of the research.