Tag Archives: Tsunami

New Zealand Earthquake – Early Perspectives

On Monday 14 November 2016 Dr Robert Muir-Wood, RMS chief research officer who is an earthquake expert and specialist in catastrophe risk management, made the following observations about the earthquake in Amberley:

SCALE
“The November 13 earthquake was assigned a magnitude 7.8 by the United States Geological Service. That makes it more than fifty times bigger than the February 2011 earthquake which occurred directly beneath Christchurch. However, it was still around forty times smaller than the Great Tohoku earthquake off the northeast coast of Japan in March 2011.”

CASUALTIES, PROPERTY DAMAGE & BUSINESS INTERRUPTION
“Although it was significantly bigger than the Christchurch earthquake, the source of the earthquake was further from major exposure concentrations. The northeast coast of South Island has a very low population and the earthquake occurred in the middle of the night when there was little traffic on the coast road. Characteristic of such an earthquake in steep mountainous terrain, there have been thousands of landslides, some of which have blocked streams and rivers – there is now a risk of flooding downstream when these “dams” break.

In the capital city, Wellington, liquefaction and slumping on man-made ground around the port has damaged some quays and made it impossible for the ferry that runs between North and South Island to dock. The most spectacular damage has come from massive landslides blocking the main coast road Highway 1 that is the overland connection from the ferryport opposite Wellington down to Christchurch. This will take months or even years to repair. Therefore it appears the biggest consequences of the earthquake can be expected to be logistical, with particular implications for any commercial activity in Christchurch that is dependent on overland supplies from the north. As long as the main highway remains closed, ferries may have to ship supplies down to Lyttelton, the main port of Christchurch.”

SEISMOLOGY
“The earthquake appears to have occurred principally along the complex fault system in the north-eastern part of the South Island, where the plate tectonic motion between the Pacific and Australian plates transfers from subduction along the Hikurangi Subduction Zone to strike-slip along the Alpine Fault System. Faults in this area strike predominantly northeast-southwest and show a combination of thrust and strike-slip motion. From its epicenter the rupture unzipped towards the northeast, for about 100-140km reaching to about 200 km to the capital city Wellington.”

WHAT NOW?
“Given the way the rupture spread to the northeast there is some potential for a follow-on major earthquake on one of the faults running beneath Wellington. The chances of a follow-on major earthquake are highest in the first few days after a big earthquake, and tail off exponentially. Aftershocks are expected to continue to be felt for months.”

MODELING
“These events occurred on multiple fault segments in close proximity to one another. The technology to model this type of complex rupture is now available in the latest RMS high-definition New Zealand Earthquake Model (2016) where fault segments may now interconnect under certain considerations.”

A Perennial Debate: Disaster Planning versus Disaster Response

In May we saw a historic first: the World Humanitarian Summit. Held in Istanbul, representatives of 177 states attended. One UN chief summarised its mission thus: “a once-in-a-generation opportunity to set in motion an ambitious and far-reaching agenda to change the way that we alleviate, and most importantly prevent, the suffering of the world’s most vulnerable people.”

And in that sentence we find one of the enduring tensions within the disaster field: between “prevention” and “alleviation.” Between on the one hand reducing disaster risk through resilience-building investments, and on the other reducing suffering and loss through emergency response.

But in a world of constrained political budgets, where should we concentrate our energies and resources: disaster risk reduction or disaster response?

How to Close the Resilience Gap

The Istanbul summit saw a new global network launched to engage business in crisis situations through “pre-positioning supplies, meeting humanitarian needs and providing resources, knowledge and expertise to disaster prevention.” It is, of course, prudent to have stockpiles of humanitarian supplies strategically placed.

But is the dialogue still too focused on response? Could we not have hoped to see a greater emphasis on driving the disaster-resilient behaviours and investments, which reduce the reliance on emergency response in the first place?

Politics & Priorities

“Cost-effectiveness” is a concept with which humanitarian aid and governmental agencies have struggled over many years. But when it comes to building resilience, it is in fact possible to cost-justify the best course of action. After all, the insurance industry, piqued by the dual surprise of Hurricane Andrew and then the Northridge earthquake, has been using stochastic models to quantify and reduce catastrophe risk since the mid-1990s.

Unfortunately risk/reward analyses are rarely straightforward in practice. This is less a failing of the models to accurately characterise complex phenomena, though that certainly is a challenge. It’s more a question of politics.

It is harder for any government to argue that spending scarce public funds on building resilience in advance of a possible disaster is money well spent. By contrast, when disaster strikes and human suffering is writ large across the media, then there is a pressing political imperative to intervene. As a result many agencies sadly allocate more funds to disaster response than to disaster prevention, even though the analytics mostly suggest the opposite would be more beneficial.

A New, Ambitious form of Public Private Partnership

But there are signs that across the different strata of government the mood is changing. The cities of San Francisco and Berkeley, for example, have begun to use catastrophe models to quantify the cost of inaction and thereby drive risk-reducing investments. For San Francisco the focus has been on protecting the city’s economic and social wealth from future sea level rise. In Berkeley, resilience models have been deployed to shore-up critical infrastructure against the threat of earthquakes.

In May, RMS held the first international workshop on how resilience analytics can be used to manage urban resilience. Attended by public officials from several continents the engagement in the topic was very high.

The role of resilience analytics to help design, implement, and measure resilience strategies was emphasized by Arnoldo Kramer, the first Chief Resilience Officer (CRO) of the largest city in the western hemisphere, Mexico City. The workshop discussion went further than just explaining how these models can be used to quantify the potential, risk-adjusted return on investment from resilience initiatives. The group stressed the role of resilience metrics in helping cities finance capital investments in new, protective infrastructure.

Stimulated by commitments under the Sendai Framework to work more closely with the private sector, lower income regions are also increasingly benefiting from such techniques – not just to inform disaster response, but also to finance the reduction of disaster risk in the first place. Indeed there are encouraging signs that these two different worlds are beginning to understand each other better. At the inaugural working group meeting of the Insurance Development Forum in Singapore last month there was a productive dialogue between the UN Development Programme and the risk transfer industry. It was clear that both sides wanted action, not just words.

Such initiatives can only serve to accelerate the incorporation of resilience analytics into existing disaster risk reduction programmes. This may be a once-in-a-generation opportunity to address the shameful gap between the economic costs of natural disasters and the fraction of those costs that are insured.

We cannot prevent natural disasters from happening. But neither can we continue to afford to spend billions of dollars picking up the pieces when they strike. I am hopeful that we will take this opportunity to bring resilience analytics into under-served societies, making them tougher, more resilient, so that when catastrophe strikes, the impact is lessened and societies can bounce back far more readily.

Harnessing Your Personal Seismometer to Measure the Size of An Earthquake

It’s not difficult to turn yourself into a personal seismometer to calculate the approximate magnitude of an earthquake that you experience. I have employed this technique myself when feeling the all too common earthquakes in Tokyo for example.

In fact, by this means scientists have been able to deduce the size of some earthquakes long before the earliest earthquake recordings. One key measure of the size of the November 1, 1755 Great Lisbon earthquake, for example, is based on what was reported by the “personal seismometers” of Lisbon.

Lisbon seen from the east during the earthquake. Exaggerated fires and damage effects. People fleeing in the foreground. (Copper engraving, Netherlands, 1756) – Image and caption from the National Information Service for Earthquake Engineering image library via UC Berkeley Seismology Laboratory

So How Do You Become a Seismometer?

As soon as you feel that unsettling earthquake vibration, your most important action to become a seismometer is immediately to note the time. When the vibrations have finally calmed down, check how much time has elapsed. Did the vibrations last for ten seconds, or maybe two minutes?

Now to calculate the size of the earthquake

The duration of the vibrations helps to estimate the fault length. Fault ruptures that generate earthquake vibrations typically break at a speed of about two kilometers per second. So, a 100km long fault that starts to break at one end will take 50 seconds to rupture. If the rupture spreads symmetrically from the middle of the fault, it could all be over in half that time.

The fastest body wave (push-pull) vibrations radiate away from the fault at about 5km/sec, while the slowest up and down and side to side surface waves travel at around 2km/second. We call the procession of vibrations radiating away from the fault the “wave-train.” The wave train comprises vibrations traveling at different speeds, like a crowd of people some of whom start off running while others are dawdling. As a result the wave-train of vibrations takes longer to pass the further you are from the fault—by around 30 seconds per 100km.

If you are very close to the fault, the direction of fault rupture can also be important for how long the vibrations last. Yet these subtleties are not so significant because there are such big differences in how the length of fault rupture varies with magnitude.

Magnitude

Fault Length Shaking duration

Mw 5

5km

2-3 seconds

Mw 6

15km

6-10 seconds

Mw 7

60km

20-40 seconds

Mw 8

200km

1-2 minutes

Mw 9 500km

3-5 minutes

Shaking intensity tells you the distance from the fault rupture

As you note the duration of the vibrations, also pay attention to the strength of the shaking.  For earthquakes above magnitude 6, this will tell you approximately how far you are away from the fault. If the most poorly constructed buildings are starting to disintegrate, then you are probably within 20-50km of the fault rupture; if the shaking feels like a long slow motion, you are at least 200km away.

Tsunami height confirms the magnitude of the earthquake

Tsunami height is also a good measure of the size of the earthquake. The tsunami is generated by the sudden change in the elevation of the sea floor that accompanies the fault rupture. And the overall volume of the displaced water will typically be a function of the area of the fault that ruptures and the displacement. There is even a “tsunami magnitude” based on the amplitude of the tsunami relative to distance from the fault source.

Estimating The Magnitude Of Lisbon 

We know from the level of damage in Lisbon caused by the 1755 earthquake that the city was probably less than 100km from the fault rupture. We also have consistent reports that the shaking in the city lasted six minutes, which means the actual duration of fault rupture was probably about four minutes long. This puts the earthquake into the “close to Mw9” range—the largest earthquake in Europe for the last 500 years.

The earthquake’s accompanying tsunami reached heights of 20 meters in the western Algarve, confirming the earthquake was in the Mw9 range.

Safety Comes First

Next time you feel an earthquake remember self-preservation should always come first. “Drop” (beneath a table or bed), “cover and hold” is good advice if you are in a well-constructed building.  If you are at the coast and feel an earthquake lasting more than a minute, you should immediately move to higher ground. Also, tsunamis can travel beyond where the earthquake is felt. If you ever see the sea slowly recede, then a tsunami is coming.

Let us know your experiences of earthquakes.

The Ever-present Threat of Tsunami: Are We Prepared?

Last week’s Mw8.3 earthquake offshore the Coquimbo region of central Chile served as a reminder that many coastal regions are exposed to earthquake and subsequent tsunami hazard.

While the extent of damage and loss of life from the recent Chile earthquake and tsunami continues to emerge and is tragic in itself, it is safe to say that things could have been much worse. After all, this is the same subduction zone that produced the 1960 Valdivia earthquake (or “Great Chilean earthquake”) 320 miles further to the south—the most powerful earthquake in recorded history.

The 1960 Valdivia earthquake had a magnitude of Mw9.6 and triggered a localized tsunami that battered the Chilean coast with waves in excess of 20 meters as well as far-field tsunami around the Pacific Ocean. Many events of M8.5+ produce tsunami that are truly global in nature and waves of several meters height can even reach coast lines more than 10,000 kilometers away from the event source, highlighting the need for international tsunami warning systems and awareness of population, city planners, and engineers in coastal areas.

 Coastlines At Risk of Tsunami

Tsunami and their deadly consequences have been with us since the beginning of mankind. What’s new, however, is the increasing awareness of the economic and insured losses that tsunami can cause. There are several mega cities in developed and emerging nations that are in the path of a future mega-tsunami, as reported by Dr. Robert Muir-Wood in his report Coastlines at Risk of Giant Earthquakes & Their Mega-Tsunami.

The 2011 earthquake and tsunami off the Pacific coast of Tohoku, Japan acted as a wake-up call to the insurance industry moving tsunami out of its quasi-niche status. With more than 15,000 lives lost, more than USD 300 billion in economic losses, and roughly USD 40 billion in insured losses, clients wanted to know where other similar high magnitude earthquakes and subsequent tsunami could occur, and what they would look like.

In response, RMS studied a multitude of high magnitude (Mw8.9-Mw9.6) event sources around the world and modeled the potential resulting tsunami scenarios. The scenarios are included in the RMS® Global Tsunami Scenario Catalog and include both historical and potential high-magnitude tsunami events that can be used to identify loss accumulations and guide underwriting decisions.

For example, below is an example output, showing the potential impact of a recurrence of the 1877 Chile Mw9.1 Earthquake (Fig 1a) and the impact of a potential future M9 scenario (Fig 1b) stemming from the Nankai Trough on the coast of Toyohashi, Japan.

Fig 1a: Re-simulation of the 1877 Chile Mw9.1 Earthquake. Coquimbo area shown. The inundation from this event would impact the entire Chilean coastline and exceed 9 meters inundation depth (further to the North). Fig 1b: M9 scenario originating on the Nankai Trough south of Japan, impacting the city of Toyohashi (population ~376 thousand), with inundation going far inland and exceeding 6 meters in height.

With rapid advances in science and engineering enabling a deeper understanding of tsunami risk, the insurance industry, city planners and local communities can better prepare for devastating tsunami, implementing appropriate risk mitigation strategies to reduce fatalities and the financial shocks that could be triggered by the next “big one.”

A Decade Later – Reconsidering The Indian Ocean Earthquake and Tsunami

This December marks the 10-year anniversary of the Indian Ocean earthquake and tsunami, a disaster that killed more than 230,000 people in 14 countries. The disaster hit Thailand and Indonesia especially hard and is considered one of the ten worst earthquakes in recorded history based on damages.

Click here for full size image

In advance of the anniversary on December 26, 2014, Dr. Robert Muir-Wood, RMS chief research officer, and Dr. Patricia Grossi, RMS senior director of global earthquake modeling, hosted their second Reddit Science AMA (Ask Me Anything). Back in October, Muir-Wood and Grossi hosted another AMA on the 25th anniversary of the Loma Prieta earthquake in the San Francisco Bay Area.

The latest Reddit thread generated almost 300 comments. Muir-Wood and Grossi discussed topics including: early warning systems for disasters like tsunamis, what variables are considered in catastrophe models, and if better building design can protect against natural disasters – particularly tsunamis. Highlights of the chat follow:

What kind of structural elements or configurations are best to combat or defend against these disasters?

Muir-Wood: There have been research studies on buildings best able to survive tsunamis. The key is to make them strong (from well engineered reinforced concrete) but with ground floor walls running parallel with the shoreline that are weak, so that the walls can be overwhelmed without threatening the whole building.

The 2004 Indian Ocean tsunami took a lot people by surprise due to the lack of a tsunami warning system even though there was a gap between the earthquake and the tsunami. If there was a tsunami warning system in place at the time would that have decreased the death toll by a lot, or not make too much of a difference considering how strong the tsunami was.

Grossi: Early warning systems are excellent tools for reducing the loss of life during an earthquake-induced tsunami event. But education is one of the easiest ways to reduce tsunami life loss. Such education needs to include knowledge of the cause of a tsunami and its association with the largest earthquakes to help individuals understand how their own observations can help them take appropriate action (e.g., seeing the water recede from the coastline). In essence, official warning systems can provide only part of the solution, as information can never be effectively disseminated to everyone along a coastline. With only 10 to 30 minutes warning in the nearfield of major tsunamis, it is imperative that people are taught to take their own action rather than wait for official instruction.

Show me the coolest tsunami video.

Muir-Wood: There are amazing videos of the Japan 2011 tsunami. I wouldn’t pick just one of them – but recommend you watch quite a few – because they are interestingly different. The most amazing feature of the tsunami is the way the water can continue to rise and rise, for five or ten minutes, apparently without end. And then how the people watching the tsunami, climb to higher locations and then realize that if it keeps rising there will be nowhere for them to go.

Was there anything we missed you wanted to discuss? Please let us know in the comments. 

Managing Risk 10 Years After the 2004 Indian Ocean Earthquake and Tsunami

On Sunday, December 26, 2004 at approximately 8 a.m. local time, a massive earthquake occurred along the Indian–Burma plate boundary off the coast of Sumatra, Indonesia. Rupturing over 1,200 km of the Sunda Trench, the magnitude of the earthquake has been estimated between M9.0 and M9.3—with the U.S. Geological Survey’s Centennial Earthquake Catalog estimating M9.1. Occurring at a fairly shallow depth—less than 30 km—the earthquake generated a basin-wide tsunami that inundated coastlines across the Indian Ocean and caused run-up waves farther afield, impacting the eastern coastline of Africa. By the end of the day, it was apparent that the event was going to emerge as one of the worst natural disasters in modern times.

Click here for full size image

Economic Toll and Recovery

Overall economic losses from the 2004 disaster were approximately $10 billion, with the majority of loss attributed to the damage in the Indonesia, Thailand, Sri Lanka, and India. The large majority of property damage was caused by the tsunami waves. Along coastlines of most of the affected countries, buildings were situated closer to sea level than is typical of higher latitudes, exacerbating the impacts.

In the aftermath of the event, the international relief efforts across the Indian Ocean were seen as fairly effective. But the longer-term recovery work in certain regions has struggled—due to the overwhelming numbers of people displaced from their homes. There are, of course, examples of well-executed reconstruction efforts. Build Change—a partner organization of RMS—has worked with tsunami survivors in Banda Aceh, Sumatra to rebuild safe, sustainable homes. Ten years after the event, evidence of the destruction wrought by the tsunami remains in the high-impacted areas.

Humanitarian Impact 

While tsunami in the Indian Ocean have certainly occurred many times before, from the perspective of modern history, the human casualties from the 2004 Indian Ocean Earthquake and Tsunami have no historical equal. More than 225,000 people lost their lives in the disaster, with most of the loss of life occurring in the near field in Sumatra, Indonesia. In Indonesia, the tsunami destroyed virtually every village, town, road, and bridge along a 170-km stretch of coast less than 10 m above sea level. Sri Lanka’s Eastern and Southern provinces were severely impacted, with fatality rate among the population within 1 km of coast between 15% and 20%. In India, entire villages in Tamil Nadu were destroyed.

In Thailand, the tsunami affected local inhabitants and foreign tourists in the densely inhabited Phuket Island. The fatalities among the tourists were a significant proportion of the overall loss of life, as many were on the beach or in hotels near the sea at the time the tsunami waves struck. In addition, the initial tsunami wave in Phuket, which was east of the rupture, began with a receding wave. Many of the tourists (not indigenous to tsunami-prone coastal regions) were unfortunately not familiar with the nature of tsunami waves. In many (but not all) tsunami, the first movement of the sea is a withdrawal. Any occasion when the sea level recedes rapidly and inexplicably should be taken as a signal for immediate flight to higher ground.

Managing Tsunami Risk in the Aftermath

The 2004 Indian Ocean Tsunami highlighted inherent vulnerabilities in the world’s coastlines and the people who live there. Coastal populations are on the increase in many parts of the world, mostly due to the exploitation of sea resources or tourism-related activities. Adequate tsunami mitigation measures— such as tsunami warning systems, education, and land use planning—can be put in place to save lives, property, and the livelihoods of those living on the coast.

Although the impact of the 2004 disaster on the global insurance industry was minimal, it alerted the world to the dangers of tsunami hazards. Worldwide response to the 2004 disaster resulted in the establishment of the Indian Ocean Tsunami Warning and Mitigation System in 2006.

Ten years hence, the world has seen two more earthquake-induced tsunami events—in the 2010 M8.8 Maule, Chile Earthquake and in the 2011 M9.0 Tohoku, Japan Earthquake—causing many clients to inquire where else in the world can events like these happen?

Chennai, India

9:30 a.m. local time

On the Indian peninsula, the hardest-hit areas were on India’s southeastern coast, in the state of Tamil Nadu, where close to 8,000 perished. Chennai, the capital of Tamil Nadu, has rebounded to become one of the Rockefeller Foundations’ “100 Resilient Cities” for its commitment to minimizing the impact of flooding in low-lying coastal areas and adopting a tsunami early warning system.

Just north of the earthquake’s epicenter, India’s Andaman and Nicobar islands were struck by waves reaching 4 to 15 m (13 to 50 ft) within 10 minutes of the earthquake. The death toll reached 7,000, with many more missing and presumed dead.

Distance from Epicenter

2,020 km

(1,260 mi)

Wave Height

5 m

(16 ft)

Time from initial rupture

3 hours

Banda Aceh, Indonesia

8:30 a.m. local time

The first wave reached Sumatra, Indonesia’s largest island, approximately 30 minutes after the initial rupture. Banda Aceh, the area hardest hit by the tsunami and closest major city to the earthquake’s epicenter, sustained more than 31,000 casualties in the city alone. Entire towns in the surrounding areas, some with populations of more than 10,000, vanished. More than 600,000 people in Aceh’s fishery and agricultural sectors lost their livelihoods.

Four times more women than men were killed—not just in Indonesia, but India and Sri Lanka as well—as many men were fishing, while women were on the beach, waiting for the fishermen to return, or at home, minding their children.

Distance from Epicenter

260 km

(160 mi)

Wave Height

30 m

(100 ft)

Time from initial rupture

30 min

Patong Beach, Thailand

9:30 a.m. local time

Tourism is one of Thailand’s key economic sectors, comprising about 12% of its overall GDP, with the greatest economic development along Thailand’s western coast. Khao Lak, Ko Phi Phi, and Phuket, with their pristine beaches, placid waters, and coral reefs, are among some of the most visited places on Earth. They were also the areas hit hardest by the tsunami.

The earthquake struck during the height of Thailand’s tourist season, causing close to 5,400 confirmed deaths, with many thousands more missing and presumed dead.

Distance from Epicenter

580 km

(360 mi)

Wave Height

6 m

(20 ft)

Time from initial rupture

1.5 hours

Galle Port, Sri Lanka

10:00 a.m. local time

Before the tsunami hit, elephants were observed running away from Patanangala beach in Yala National Park, directly in the tsunami’s path. Flamingos, goats, and buffaloes also moved to higher ground. All but two water buffaloes were unharmed.

When the waves came, Sri Lanka’s eastern and southern provinces were the hardest hit. In the coastal town of Telwatta, the tsunami struck an overcrowded train packed with passengers for the Buddhist full moon and Christmas holiday weekend. More than 1,700 lives were lost in what became the worst humanitarian disaster in railroad history.

Distance from Epicenter

1,750 km

(1,100 mi)

Wave Height

6 m

(20 ft)

Time from initial rupture

3 hours

Wave Height

6 m

(20 ft)

Northern Sumatra, West Coast

7:58 a.m. local time

The M9.1 earthquake struck 160 km (100 mi) off the northwest coast of Sumatra, Indonesia, generating the deadliest tsunami in history. With a rupture length of more than 1,200 km (750 mi), the earthquake released energy equivalent to 475 megatons of TNT, and shot a massive water column into the air.

The water settled back into the open ocean as a barely perceptible swell of only 50 cm (1.6 feet)—but moved at speeds of more than 600 km/hr (370 mph). It slowed toward the coast, inundating Sumatra with waves of up to 30 m (100 feet), leaving more than 225,000 people missing or presumed dead, and displacing 1.5 million more.

Countries impacted

14

Total insured losses

$1 billion

Total economic losses

$10 billion

RMS To Launch Global Tsunami Scenario Catalog

The 2011 Tohoku earthquake and its accompanying mega-tsunami highlighted how a single magnitude 9.0 (Mw9) tsunami could impact multiple regions and lines of business. The size of the earthquake was considered beyond what was possible on this plate boundary, and there are many areas worldwide where a massive earthquake and accompanying tsunami could impact coastal exposures over a very wide area.

Global coastal exposure is increasing rapidly including port cities, refineries, power plants, hotels and beach resorts. On regions around the Pacific and parts of the Indian and Atlantic Oceans, some of these exposure accumulations are at frontline risk from the mega-tsunamis that would accompany magnitude 9.0 (Mw9) earthquakes.

Later this year, RMS will release a Global Tsunami Scenario Catalog to provide (re)insurers with a broad and relevant set of tsunami scenarios that include both local and ocean-wide impacts. The tsunamis scenarios have been generated by modeling fault rupture and sea floor deformation associated with earthquakes on the principal subduction zones worldwide, with magnitudes ranging between M8.0-9.5.

For each scenario the tsunami is modeled in three stages – a) the initial generation of the water level changes caused by sudden movements in the configuration of the seafloor, b) tsunami wave propagation, and c) the flooding inundation of coastlines.

For each scenario the tsunami flood is represented as the elevation of the water level at each onshore location in the path of a tsunami. The tsunami flood data also includes the maximum expected inundation depth of tsunami flooding so that users can estimate the level of destruction to different building categories. The tsunami modeling capability has been extensively tested to show the method reproduces the observed coastal water heights from recent tsunamis.

A key element of the work to create the new Global Tsunami Scenario Catalog involved identifying where Mw9 earthquakes had the potential to occur, and hence which were the coastal regions at risk from mega- tsunami. These regions include cities with high insurance penetration such as Hong Kong and Macao, the main Taiwanese port of Kaohsiung, the island of Barbados, as well as Muscat, Oman. Our research also shows that a mega-tsunami as large as Tohoku could even occur in the Eastern Mediterranean – and in fact a mega-tsunami was generated in this region in 365 A.D. A repeat of such a tsunami could impact a wide stretch of coastal cities from Alexandria, Egypt to Kalamata, Greece and Antalya, Turkey.

The Tohoku earthquake and tsunami surprised the world because it occurred on a plate boundary that was not considered capable of producing a giant earthquake. The lessons from Tohoku should be applied to other ‘dormant’ subduction zone plate boundaries worldwide where M9 earthquakes have the potential to occur even though they have not previously been experienced in the past few hundred years of history. The region-wide loss correlations associated with some of these events have the potential to affect multiple lines of property and marine exposures in diverse coastal locations, potentially spanning several countries in a single loss. (Re)insurers wishing to manage their regional coastal exposures should be testing their exposure accumulations against a credible set of the largest-scale earthquake and tsunami scenarios.

The Dangerous City of Tacloban

The city of Tacloban, on the island of Leyte, is the largest city in the eastern Visayas region of the central Philippines. In a 2010 survey by the Asian Institute of Management, Tacloban was ranked fifth in the “most competitive” cities in the Philippines, and second in the class of “emerging cities.” Before Haiyan’s storm surge, the city was thriving, with only one third the national average poverty levels.

However, from the natural hazards perspective Tacloban would also be high up on a list of the most dangerous medium size cities in the world.

Tacloban faces east into the tropical Pacific where there is the largest, deepest and hottest pool of ocean water on the planet, fuel for cooking up intense super typhoons, and sustaining their intensity all the way to landfall. More significantly the port city is located in the apex (or “armpit”) of a funnel-shaped coastline – where the eastern coast of the island of Leyte meets the southern coast of the island of Samar. Although the 2km wide “San Juanico” channel separates these islands, in a fast westerly moving typhoon, this channel cannot relieve the large dome of water pushed ahead of the storm.

Funnel shaped coastlines are notorious for concentrating and amplifying tropical cyclone storm surges. New York City is situated at the apex of the funnel-shaped coastline where New Jersey meets Long Island, amplifying the surge from Super-storm Sandy. Osaka in Japan is also at the apex of funnel coastline. However intense typhoons pass close to Leyte far more often than intense hurricanes come to New York or Japan.

The ground on which the quarter of a million population city of Tacloban has grown up is remarkably flat and only a meter or two above high tide level. A 4-6 meter storm surge and its accompanying waves can penetrate far inland, ripping houses off their foundations for several blocks, just as happened in the cities along the southern coast of the State of Mississippi in Hurricane Katrina.

Tacloban is built on a former wave-cut platform, at the foot of active cliffs, which has become raised out of the sea by active tectonics. For the city is also located in the frontline of a plate boundary.

Offshore to the east, less than 80km from the neighbouring island of Samar, a deep sea trench, marks where the Philippines Sea plate moves down beneath the Philippines, at around 50mm per year. The 1300 km NNW-SSE Philippines subduction zone appears to be locked, and has not broken in a major earthquake through the past four hundred years, since the start of Spanish colonial rule.

If, as is suspected, the Philippines subduction zone is capable of generating a giant Mw9 earthquake, then this will be accompanied by a large tsunami, as in Sumatra 2004 and Tohoku, Japan in 2011. Tacloban is very much in the frontline of such a tsunami – the biggest city, on low ground, facing the open Pacific. A tsunami at 10 m or more could cause more casualties and destruction even than the 2013 storm surge.

Tacloban city was founded as a fishing village and more recently achieved fame as the birthplace of Imelda Marcos. Some parts of its history are obscure, in particular when it first became a municipality, as the records were all destroyed in a previous typhoon. The name Tacloban has the potential to recur on the list of future catastrophes. Only action in reconstruction, relocating the city away from the low lying coast, can reduce that potential.