Tag Archives: Earthquake

“Italy is Stronger than any Earthquake”

Those were the words of the then Italian Prime Minister, Matteo Renzi, in the aftermath of two earthquakes on the same day, October 26, 2016. As a statement of indomitable defiance at a scene of devastation it suited the political and public mood well. But the simple fact is there is work to do, because Italy is not as strong as it could be in its resilience to earthquakes.

There’s a long history of powerful seismic activity in the central Apennines: only recently we’ve seen L’Aquila (2009, Mw6.3), Amatrice (August 2016, Mw6.0), two earthquakes in the area near Visso (October 2016, Mw 5.4 and 5.9) and Norcia (October 2016, Mw6.5). These have resulted in hundreds of fatalities, mainly attributed to widespread collapse of old buildings, emphasizing that earthquakes don’t kill people – buildings do. Whilst Italy’s Civil Protection Department provides emergency management and support after earthquakes, there is too little insurance help for the financial resiliency of the communities most affected by all these events. While the oft-repeated call for earthquake insurance to be compulsory continues to be politically unobtainable, one way it could be spread more widely is through effective modeling. And RMS expertise can help with this, allowing the market to better understand the risk and so build resilience.

Examining High Building Fragility

The two most significant factors for earthquake risk in Italy are (i) construction materials and (ii) the age of the buildings. The majority of the damaged and destroyed buildings were made from unreinforced masonry, and built prior to the introduction of the most recent seismic design and building codes, making them particularly susceptible. With the RMS® Europe Earthquake model capturing both the variations in construction types and age, as well as other vulnerability factors, (re)insurers can accurately reflect the response of different structures to earthquakes.  This allows the models to be used to evaluate the cost benefits of retrofitting buildings.  RMS has worked with the Italian National Institute for Geophysics and Volcanology (INGV) to see how such analyses could be used to optimize the allocation of public funds for strengthening older buildings, thereby reducing future damage and costs.

Seismic Risk Assessment

The high-risk zone of the central Apennines is described well by probabilistic seismic hazard assessment (PSHA) maps, which show the highest risks in that region resulting from the movement of tectonic blocks that produce the extensional, ‘normal’ faulting observed. The maps also show earthquake risk throughout the rest of Italy. RMS worked with researchers from INGV to develop our view of risk in 2007, based on the latest available databases at that time, including active faults and earthquake catalogs. The resulting hazard model produces a countrywide view of seismic hazard that has not been outdated by newer studies, such as the 2009 INGV Seismic Hazard Map and the 2013 European Seismic Hazard Map published by the SHARE consortium, as shown below:

blog_italy-eq

The Route to Increased Resiliency

Increasing earthquake resiliency in Italy should also involve further development of the private insurance market. The seismic risk in Italy is relatively high for western Europe, whilst the insurance penetration is low, even outside the central Apennines. For example, in 2012, there were two large earthquakes in the Emilia-Romagna region of the Po valley, where there are higher concentrations of industrial and commercial risks. Although the type of faults and risks vary by region, such as the potential impact of liquefaction, the RMS model captures such variations in risk and can be used for the development of risk-based pricing and products for the expansion of the insurance market throughout the country.

Whilst Italy’s seismic events in October caused casualties on a lesser scale than might have been, the extent of the damage highlights once again the prevalence of earthquake risk. It is only a matter of time before the next disaster strikes, either in the Central Apennines or elsewhere. When that happens, the same questions will be asked about how Italy could be made more resilient. But if, by then, the country’s building stock is being made less susceptible and the private insurance market is growing markedly, then Italy will be able to say, with justification, it is becoming stronger than any earthquake.

Earthquake Hazard: What Has New Zealand’s Kaikoura Earthquake Taught Us So Far?

The northeastern end of the South Island is a tectonically complex region with the plate motion primarily accommodated through a series of crustal faults. On November 14, as the Kaikoura earthquake shaking began, multiple faults ruptured at the same time culminating in a Mw 7.8 event (as reported by GNS Science).

The last two weeks have been busy for earthquake modelers. The paradox of our trade is that while we exist to help avoid the damage this natural phenomenon causes, the only way we can fully understand this hazard is to see it in action so that we can refine our understanding and check that our science provides the best view of risk. Since November 14 we have been looking at what Kaikoura tells us about our latest, high-definition New Zealand Earthquake model, which was designed to handle such complex events.

Multiple-Segment Ruptures

With the Kaikoura earthquake’s epicenter at the southern end of the faults identified, the rupture process moved from south to north along this series of interlinked faults (see graphic below). Multi-fault rupture is not unique to this event as the same process occurred during the 2010 Mw 7.2 Darfield Earthquake. Such ruptures are important to consider in risk modeling as they produce events of larger magnitude, and therefore affect a larger area, than individual faults would on their own.

Map showing the faults identified by GNS Sciences as experiencing surface fault rupture in the Kaikoura Earthquake.
Source: http://info.geonet.org.nz/display/quake/2016/11/16/Ruptured +land%3A+observations+from+the+air

In keeping with the latest scientific thinking, the New Zealand Earthquake HD Model provides an expanded suite of events that represent complex ruptures along multiple faults. For now, these are included only for areas of high slip fault segments in regions with exposure concentrations, but their addition increases the robustness of the tail of the Exceedance Probability curve, meaning clients get a better view of the risk of the most damaging, but lower probability events.

Landsliding and Liquefaction

While most property damage has been caused directly by shaking, infrastructure has been heavily impacted by landsliding and, to a lesser extent, liquefaction. Landslides and slumps have occurred across the region, most notably over Highway 1, an arterial route. The infrastructure impacts of the Kaikoura earthquake are a likely dress rehearsal for the expected event on the Alpine Fault. This major fault runs 600 km along the western coast of the South Island and is expected to produce an Mw 8+ event with a probability of 30% in the next 50 years, according to GNS Science.

As many as 80 – 100,000 landslides have been reported in the upper South Island, with some creating temporary dams over rivers and in some cases temporary lakes (see below). These dams can fail catastrophically, sending a sudden increase of water flow down the river.

 

picture2

Examples of rivers blocked by landslides photographed by GNS Science researchers.

Source: http://info.geonet.org.nz/display/quake/2016/11/18/ Landslides+and+Landslide+dams+caused +by+the+Kaikoura+Earthquake

 

 

 

 

 

 

 

 

Liquefaction occurred in discrete areas across the region impacted by the Kaikoura earthquake. The Port of Wellington experienced both lateral and vertical deformation likely due to liquefaction processes in reclaimed land. There have been reports of liquefaction near the upper South Island towns (Blenheim, Seddon, Ward), but liquefaction will not be a driver of loss in the Kaikoura event to the extent it was in the Christchurch earthquake sequence.

RMS’ New Zealand Earthquake HD Model includes a new liquefaction component that was derived using the immense amount of new borehole data collected after the Canterbury Earthquake Sequence in 2010-2011. This new methodology considers additional parameters, such as depth to the groundwater table and soil-strength characteristics, that lead to better estimates of lateral and vertical displacement. The HD model is the first probabilistic model with a landslide susceptibility component for New Zealand.

Tsunami

The Kaikoura Earthquake generated tsunami waves that were observed in Kaikoura at 2.5m, Christchurch at 1m, and Wellington at 0.5m. The tsunami waves arrived in Kaikoura significantly earlier than in Christchurch and Wellington indicating that the tsunami was generated near Kaikoura. The waves were likely generated by offshore faulting, but also may be associated with submarine landsliding. Fortunately, the scale of the tsunami waves did not produce significant damage. RMS’ latest New Zealand Earthquake HD Model captures tsunami risk due to local ocean bottom deformation caused by fault rupture, and is the first model in the New Zealand market to do this, that is built from a fully hydrodynamic model.

Next Generation Earthquake Modeling at RMS

Thankfully the Kaikoura earthquake seems to have produced damage that is lower than we might have seen had it hit a more heavily populated area of New Zealand with greater exposures – for detail on damage please see my other blog on this event.

But what Kaikoura has told us is that our latest HD model offers an advanced view of risk. Released only in September 2016, it was designed to handle such a complex event as the Kaikoura earthquake, featuring multiple-segment ruptures, a new liquefaction model at very high resolution, and the first landslide susceptibility model for New Zealand.

New Zealand’s Kaikoura Earthquake: What Have We Learned So Far About Damage?

The Kaikoura Earthquake of November 14 occurred in a relatively low population region of New Zealand, situated between Christchurch and Wellington. The largest town close to the epicentral region is Blenheim, with a population near 30,000.

Early damage reports indicate there has been structural damage in the northern part of the South Island as well as to numerous buildings in Wellington. While most of this has been caused directly by shaking, infrastructure and ports across the affected region have been heavily impacted by landsliding and, to a lesser extent, liquefaction. Landslides and slumps have occurred across the northeastern area of the South Island, most notably over Highway 1, severing land routes to Kaikoura – a popular tourist destination.

The picture of damage is still unfolding as access to badly affected areas improves. At RMS we have been comparing what we have learned from this earthquake to the view of risk provided by our new, high-definition New Zealand Earthquake model, which is designed to improve damage assessment and loss quantification at location-level resolution.

No Damage to Full Damage

The earthquake shook a relatively low population area of the South Island and, while it was felt keenly in Christchurch, there have been no reports of significant damage in the city. The earthquake ruptured approximately 150 km along the coast, propagating north towards Wellington. The capital experienced ground shaking intensities at the threshold for damage, producing façade and internal, non-structural damage in the central business district. Although the shaking intensities were close to those experienced during the Cook Strait sequence in 2013, which mostly affected short and mid-rise structures, the longer duration and frequency content of the larger magnitude Kaikoura event has caused more damage to taller structures which have longer natural periods.

From: Wellington City Council

Within Wellington, cordons are currently in place around a few buildings in the CBD (see above) as engineers carry out more detailed inspections. Some are being demolished or are set to be, including a nine-story structure on Molesworth Street and three city council buildings. It should be noted that most of the damage has been to buildings on reclaimed land close to the harbor where ground motions were likely amplified by the underlying sediments.

From: http://www.stuff.co.nz/national/86505695/quakehit-wellington-building-at-risk-of-collapse-holds-up-overnight; The building on Molesworth street before the earthquake (L) and on Tuesday (R).

From: http://www.stuff.co.nz/national/86505695/quakehit-wellington-building-at-risk-of-collapse-holds-up-overnight; The building on Molesworth street before the earthquake (L) and after on November 16 (R).

Isolated incidences of total damage in an area of otherwise minor damage demonstrate why RMS is moving to the new HD financial modeling framework. The RMS RiskLink approach applies a low mean damage ratio across the area, whereas RMS HD damage functions allow for zero or total loss – as well as a distribution in between which is sampled for each event for each location. The HD financial modeling framework is able to capture a more realistic pattern of gross losses.

Business Interruption

The Kaikoura Earthquake will produce business interruption losses from a variety of causes such as direct property or content damages, relocation costs, or loss of access to essential services (i.e. power and water utilities, information technology) that cripple operations in otherwise structurally sound buildings. How quickly businesses are able to recover depends on how quickly these utilities are restored. Extensive landslide damage to roads means access to Kaikoura itself will be restricted for months. The New Zealand government has announced financial assistance packages for small business to help them through the critical period immediately after the earthquake. Similar assistance was provided to businesses in Christchurch after the Canterbury Earthquake Sequence in 2010-2011.

That earthquake sequence and others around the world have provided valuable insights on business interruption, allowing our New Zealand Earthquake HD model to better capture these impacts. For example, during the Canterbury events, lifelines were found to be repaired much more quickly in urban areas than in rural areas, and areas susceptible to liquefaction were associated with longer down times due to greater damage to underground services. The new business interruption model provides a more accurate assessment of these risks by accounting for the influence of both property and contents damage as well as lifeline downtime.

It remains to be seen how significant any supply chain or contingent business interruption losses will be. Landslide damage to the main road and rail route from Christchurch to the inter-island ferry terminal at Picton has disrupted supply routes across the South Island. Alternative, longer routes with less capacity are available.

Next Generation Earthquake Modeling at RMS

RMS designed the update to its New Zealand Earthquake High Definition (HD) model, released in September 2016, to enhance location-level damage assessment and improve the gross loss quantification with a more realistic HD financial methodology. The model update was validated with billions of dollars of claims data from the 2010-11 Canterbury Earthquake Sequence.

Scientific and industry lessons learned following damaging earthquakes such as last month’s in Kaikoura and the earlier event in Christchurch increase the sophistication and realism of our understanding of earthquake risk, allowing communities and businesses to shift and adapt – so becoming more resilient to future catastrophic events.

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.”

Searching for Clues After the Ecuador Earthquake

Reconnaissance work is built into the earthquake modeler’s job description – the backpack is always packed and ready. Large earthquakes are thankfully infrequent, but when they do occur, there is much to be learned from studying their impact, and this knowledge helps to improve risk models.

An RMS reconnaissance team recently visited Ecuador. Close to 7pm local time, on April 16, 2016, an Mw7.8 earthquake struck between the small towns of Muisne and Pedernales on the northwestern coast of Ecuador. Two smaller, more recent earthquakes have also impacted the area, on July 11, 2016 an Mw5.8 and Mw6.2, fortunately with no significant damage.

April’s earthquake was the strongest recorded in the country since 1979 and, at the time of writing, the strongest earthquake experienced globally so far in 2016. The earthquake caused more than 650 fatalities, more than 17,600 injuries, and damage to more than 10,000 buildings.

Two weeks after the earthquake, an RMS reconnaissance team of engineers started their work, visiting five cities across the affected region, including Guayaquil, Manta, Bahía de Caráquez, Pedernales, and Portoviejo. Pedernales was the most affected, experiencing the highest damage levels due to its proximity to the epicenter, approximately 40km to the north of the city.

Sharing the Same Common Vulnerability

The majority of buildings in the affected region were constructed using the same structural system: reinforced concrete (RC) frames with unreinforced concrete masonry (URM) infill. This type of structural system relies on RC beams and columns to resist earthquake shaking, with the walls filled in with unreinforced masonry blocks. This system was common across residential, industrial, and commercial properties and across occupancies, from hospitals and office buildings to government buildings and high-rise condominiums.

URM infill is particularly susceptible to damage during earthquakes, and for this reason it is prohibited by many countries with high seismic hazard. But even though Ecuador’s building code was updated in 2015, URM infill walls are still permitted in construction, and are even used in high-end residential and commercial properties.

Without reinforcing steel or adequate connection to the surrounding frame, the URM often cracks and crumbles during strong earthquake shaking. In some cases, damaged URM on the exterior of buildings falls outward, posing safety risks to people below. And for URM that falls inward, besides posing a safety risk, it often causes damage to interior finishes, mechanical equipment, and contents.

Across the five cities, the observed damage ranged from Modified Mercalli Intensity (MMI) 7.0-9.0. For an MMI of 7.0, the damage equated to light to moderate damage of URM infill walls, and mostly minimal damage to RC frames with isolated instances of moderate-to-heavy damage or collapse. An MMI of 9.0, which based on RMS observations, occurred in limited areas, meant moderate to heavy damage of URM infill walls and slight to severe damage or collapse to RC frames.

While failure of URM infill was the most common damage pattern observed, there were instances of partial and even complete structural collapse. Collapse was often caused, at least in part by poor construction materials and building configurations, such as vertical irregularities, that concentrated damage in particular areas of buildings.

Disruption to Business and Public Services

The RMS team also examined disruption to business and public services caused by the earthquake. A school in Portoviejo will likely be out of service for more than six months, and a police station in Pedernales will likely require more than a year of repair work. The disruption observed by the RMS team was principally due to direct damage to buildings and contents. However, there was some disruption to lifeline utilities such as electricity and water in the affected region, and this undoubtedly impacted some businesses.

RMS engineers also visited four public hospitals and clinics, with damage ranging from light to complete collapse. The entire second floor of a clinic in Portoviejo collapsed. A staff doctor told RMS that the floor was empty at the time and all occupants, including patients, evacuated safely.

Tourism was disrupted, with a few hotels experiencing partial or complete collapse. In some cases, even lightly damaged and unaffected hotels were closed as they were within cordoned-off zones in Manta or Portoviejo.

Tuna is an important export product for Ecuador. Two plants visited sustained minor structural damage, with unanchored machinery requiring repositioning and recalibration. One tuna processing plant reached 100% capacity just 16 days after the earthquake. Another in Manta reached 85% capacity about 17 days after the earthquake, and full capacity was expected within one month.

The need for risk differentiation

Occupancy, construction class, year built, and other building characteristics influence the vulnerability of buildings and, consequently, the damage they sustain during earthquakes. Vulnerability is so important in calculating damage from earthquakes that RMS model developers go to great lengths to ensure that each country’s particular engineering and construction practices are accurately captured by the models. This approach enables the models to differentiate risk across thousands of different factors.

Residential insurance penetration in Ecuador is still relatively low for commercial buildings and privately owned or financed homes, but higher amongst government-backed mortgages, as these require insurance. The knowledge gained from reconnaissance work is fundamental to our understanding of earthquake risk and informs future updates to RMS models. Better models will improve the insurance industry’s understanding and management of earthquake risk as insurance penetration increases both here and around the world.

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.

Liquefaction: a wider-spread problem than might be appreciated

Everyone has known for decades that New Zealand is at serious risk of earthquakes. In his famous Earthquake Book, Cuthbert Heath, the pioneering Lloyd’s non-marine underwriter, set the rate for Christchurch higher than for almost any other place, back in 1914. Still, underwriters were fairly blasé about the risk until the succession of events in 2010-11 known as the Canterbury Earthquake Sequence (CES).

New Zealand earthquake risk had been written by reinsurers usefully for diversification; it was seen as uncorrelated with much else, and no major loss event had occurred since the Edgecumbe earthquake in 1987. Post-CES, however, the market is unrecognizable. More importantly, perhaps, it taught us a great deal about liquefaction, a soil phenomenon which can multiply the physical damage caused by moderate to large earthquakes, and is a serious hazard in many earthquake zones around the world, particularly those with near water bodies, water courses, and the ocean.

The unprecedented liquefaction observation data collected during the CES made a significant contribution to our understanding of the phenomenon, and the damage it may cause. Important to know is that the risk is not limited to New Zealand. Liquefaction has been a significant cause of damage during recent earthquakes in the United States, such as the 1989 Loma Prieta earthquake in the San Francisco Bay area and the devastating 1964 earthquake in Alaska which produced very serious liquefaction around Anchorage. Unsurprisingly, other parts of the world are also at risk, including the coastal regions of Japan, as seen in the 1995 Kobe and 1964 Niigata earthquakes, and Turkey. The 1999 Izmit earthquake produced liquefaction along the shorelines of Izmit Bay and also in the inland city of Adapazari situated along the Sakarya River. The risk is as high in regions that have not experienced modern earthquakes, such as the Seattle area, and in the New Madrid seismic zone along the Mississippi River.

2011 Lyttelton: observed and learned

Five years ago this week, the magnitude 6.3 Lyttelton (or Christchurch) Earthquake, the most damaging of the sequence, dealt insured losses of more than US $10 billion. It was a complex event both from scientific and industry perspectives. A rupture of approximately 14 kilometers occurred on a previously unmapped, dipping blind fault that trends east to northeast.[1] Although its magnitude was moderate, the rupture generated the strongest ground motions ever recorded in New Zealand. Intensities ranged between 0.6 and 1.0 g in Christchurch’s central business district, where for periods between 0.3 and 5 seconds the shaking exceeded New Zealand’s 500-year design standard.

The havoc wrought by the shaking was magnified by extreme liquefaction, particularly around the eastern suburbs of Christchurch. Liquefaction occurs when saturated, cohesion-less soil loses strength and stiffness in response to a rapidly applied load, and behaves like a liquid. Existing predictive models did not capture well the significant contribution of extreme liquefaction to land and building damage.

Figure 1: The photo on the left shows foundation failure due to liquefaction which caused the columns on the left side of the building to sink. The photo on the right shows a different location with evident liquefaction (note the silt around columns) and foundation settlement.

Structural damage due to liquefaction and landslide accounted for a third of the insured loss to residential dwellings caused by the CES. Lateral spreading and differential settlement of the ground caused otherwise intact structures to tilt beyond repair. New Zealand’s government bought over 7,000 affected residential properties, even though some suffered very little physical damage, and red-zoned entire neighborhoods as too hazardous to build on.

Figure 2: Christchurch Area Residential Red-Zones And Commercial Building Demolitions (Source: Canterbury Earthquake Recovery Authority (CERA), March 5, 2015).

Incorporating the learnings from Christchurch into the next model update

A wealth of new borehole data, ground motion recordings, damage statistics, and building forensics reports has contributed to a much greater understanding of earthquake hazard and local vulnerability in New Zealand. RMS, supported by local geotechnical expertise, has used the data to redesign completely how liquefaction is modeled. The RMS liquefaction module now considers more parameters, such as depth to groundwater table and certain soil-strength characteristics, all leading to better predictive capabilities for the estimate of lateral and vertical displacement at specific locations. The module now more accurately assesses potential damage to buildings based on two potential failure modes.

The forthcoming RMS New Zealand Earthquake HD Model includes pre-compiled events that consider the full definition of fault rupture geometry and magnitude. An improved distance-calculation approach enhances near-source ground motion intensity predictions. This new science, and other advances in RMS models, serve a vital role in post-CES best practice for the industry, as it faces more regulatory scrutiny than ever before.

Liquefaction risk around the world

Insurers in New Zealand and around the world are doing more than ever to understand their earthquake exposures, and to improve the quality of their data both for the buildings and the soils underneath them. In tandem, greater market emphasis is being placed on understanding the catastrophe models. Key, is the examination of the scientific basis for different views of risk, characterized by a deep questioning of the assumptions embedded within models. In the spotlight of ever-increasing scrutiny from regulators and stakeholders, businesses must now be able to articulate the drivers of their risk, and demonstrate that they are in compliance with solvency requirements. Reference to Cuthbert Heath’s rate—or the hazard as assessed last year—is no longer enough.

[1] Bradley BA, Cubrinovski M.  Near-source strong ground motions observed in the 22 February 2011 Christchurch Earthquake.  Seismological Research Letters 2011. Vol. 82 No. 6, pp 853-865.

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 Curious Story of the “Epicenter”

The word epicenter was coined in the mid-19th century to mean the point at the surface above the source of an earthquake. After discarding explanations, such as “thunderstorms in caverns” or “electrical discharges,” earthquakes were thought to be underground chemical explosions.

Source: USGS

Two historical earthquakes—1891 in Japan and 1906 in California—made it clear that a sudden movement along a fault caused earthquakes. The fault that broke in 1906 was almost 300 miles long. It made no sense to consider the source of the earthquake as a single location. The word epicenter should have gone the way of other words attached to redundant scientific theories like “phlogiston” or the “aether.”

But instead the term epicenter underwent a strange resurrection.

With the development of seismic recorders at the start of the 20th century, seismologists focused on identifying the time of arrival of the first seismic waves from an earthquake. By running time backwards from the array of recorders they could pinpoint where the earthquake initiated. The point at the surface above where the fault started to break was termed the “epicenter.” For small earthquakes, the fault will not have broken far from the epicenter, but for big earthquakes, the rupture can extend hundreds of kilometres. The vibrations radiate from all along the fault rupture.

In the early 20th century, seismologists developed direct contacts with the press and radio to provide information on earthquakes. Savvy journalists asked for the location of the “epicenter”—because that was the only location seismologists could give. The term “epicenter” entered everyday language: outbreaks of disease or civil disorder could all have “epicenters.” Graphics departments in newspapers and TV news now map the location of the earthquake epicenter and run rings around it—like ripples from a stone thrown into a pond—as if the earthquake originates from a point, exactly as in the chemical explosion theory 150 years ago.

The bigger the earthquake, the more misleading this becomes. The epicenter of the 2008 Wenchuan earthquake in China was at the southwest end of a fault rupture almost 250km long. In the 1995 Kobe, Japan earthquake, the epicenter was far to the southwest even though the fault rupture ran right through the city. In the great Mw9 2011 Japan earthquake, the fault rupture extended for around 400km. In each case TV news showed a point with rings around it.

In the Kathmandu earthquake in April 2015, television news showed the epicenter as situated 100km to the west of the city, but in fact the rupture had passed right underneath Kathmandu. The practice is not only misleading, but potentially dangerous. In Nepal the biggest aftershocks were occurring 200km away from the epicenter, at the eastern end of the rupture close to Mt Everest.

How can we get news media to stop asking for the epicenter and start demanding a map of the fault rupture? The term “epicenter” has an important technical meaning in seismology; it defines where the fault starts to break. For the last century it was a convenient way for seismologists to pacify journalists by giving them the easily calculated location of the epicenter. Today, within a few hours, seismologists can deliver a reasonable map of the fault rupture. More than a century after the discovery that a fault rupture causes earthquakes, it is time this is recognized and communicated by the news.

Earthquake’s “Lightning”

Thunder is the noise made by the phenomenon of lightning. It was only in the mid 20th Century that we learned why lightning is so noisy. Even Aristotle thought thunder was caused by clouds bumping into one another. We now know that thunder is generated by the supersonic thermal expansion of air, as the electrical charge arcs through the atmosphere.

Like thunder, the earthquake is also a noise; it is so low pitched that it is almost inaudible, but so loud that it can cause buildings to shake themselves to bits. So what is the name of the phenomenon that produces this quaking noise?

We tend to lazily call it the “earthquake,” but that is as wrong as calling lightning “thunder.” We need a distinct word to describe the source of earthquake vibrations, equivalent to lightning being the cause of thunder. We need a word to describe earthquake’s “lightning.”

Like a spontaneously firing crossbow, the Earth’s crust is slowly loaded with strain and then suddenly discharged into fault displacement. Since 2000 we have become better at observing the two halves of the process.

One half concerns the sudden release of strain accumulated during hundreds or thousands of years over a large volume of the crust. We can now observe this strain release from continuous GPS measurements or from inter-ferometric analysis of synthetic aperture radar images.

The second half of the process is the distribution of displacement along the fault, which can now be reconstructed by inverting the full signature of vibrations at each seismic recorder.

Focusing on the earthquake vibrations means that we forget all the other consequences of the regional strain release.

For example, hot springs stopped across the whole of northern Japan following the 2011 Tohoku earthquake because the extensional release of compressional strain diverted the water to fill up all the cracks. In the elastic rebound of prolonged extension, half a cubic kilometer of water was squeezed out of the crust over nine months in the region around the last big extensional fault earthquake in the US in Idaho in 1983.

Sudden strain can cause significant land level changes; the city of Valdivia sunk 8 feet in the 1960 Chile earthquake, while Montague Island off the coast of Alaska rose 30 feet in the 1964 Great Alaska earthquake. Whether your building plot is now below sea level or your dock is high out of the sea, land level changes can themselves be a big source of loss.

Then, there are the tsunamis generated by all the regional changes in seafloor elevation due to earthquakes. In the 2011 Tohoku Japan earthquake, it was the subsequent tsunami contributed almost half the damage and almost all of the casualties.

So, what is the name of earthquake’s “lightning?” “Elastic rebound” describes one half of the process and “fault rupture” the other half. But no word combines the two. A word combining the two would have to mean “the sudden transformation of stored strain into fault displacement.” We could have called the origin of thunder “the sudden discharge of electrical charge between the ground and clouds,” but “lightning” slips more easily off the tongue.

There could be a competition to coin a new word to describe the earthquake generation process. Perhaps “strainburst,” “faultspring,” or, as the underground equivalent of lightning, “darkning.” We are scientifically bereft without a word for earthquake’s “lightning.”