Tag Archives: earthquake modeling

It’s What’s On The Inside That Counts

Most people use this phrase when it comes to judging a person’s character, but few would think to use it when assessing a building’s preparedness against damage from seismic activity. Cracked foundations, toppled walls, and collapsed buildings are normally what comes to mind when envisioning a building damaged from an earthquake; and while they are of course costly to repair, surprisingly this type of damage is not the main cause of loss to insurers.

Over 70 percent of a building’s value comes from non-structural elements such as internal and external cladding, interior walls, glazing and the internal fit-out, such as heating and air conditioning systems, pipes, ceiling support systems, and lighting. Building codes dictate how these internal systems should be installed and detail the necessary seismic restraints to keep them in place in the event of intense ground shaking. Failure to properly implement these measures can result in significant damage and expensive payouts, even if the structural integrity and exterior of the building remains intact. Recent global earthquake events such as Kaikoura in 2016 reflect this and have shown that non-structural damage drives claims.

Continue reading

The California Earthquake Authority (CEA) and RMS Co-host Webinar to Share Insights on California Earthquake Risk Using North America Earthquake Version 17.0

Together with the California Earthquake Authority (CEA), RMS co-hosted a webinar on May 17 for the CEA’s global panel of catastrophe reinsurers to explore how new earthquake science and RMS modeling impacts the CEA and its markets. The CEA is one of the largest earthquake insurance programs in the world with nearly one million policyholders throughout California. In the webinar, we analyzed and shared insights about the risk to the CEA book using the new Version 17 RMS North America Earthquake Models which was just released on April 28.

Continue reading

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.

Cultivating Resilience Through Catastrophe Modeling

Through our partnership with the Rockefeller Foundation’s 100 Resilient Cities initiative, RMS is tasked with helping cities around the world become more resilient to the physical, social, and economic challenges that are a growing part of the 21st century. Our recent engagement with the city of Berkeley, California highlighted how modeling can be used to help a city acutely understand its risk and create policy that accurately protects against it, thereby helping to save lives of vulnerable populations.

RMS completed a dual-view seismic analysis for the city of Berkeley. The first was a city-wide analysis showcasing the vulnerability of all neighborhoods across Berkeley under various magnitude scenarios. RMS then completed a building-level study on the city’s critical infrastructure of care and shelter sites. These structures are the city’s emergency shelters and are intended to house all displaced residents after an earthquake. Our analysis concluded that these shelters are located in areas susceptible to higher than average damage, indicating that these facilities would be critical to surrounding neighborhoods following an earthquake. Furthermore, we found that in their current construction state, these buildings performed worse than average in all seismic scenarios modeled and that retrofitting these buildings was an economical way to improve building performance.

This RMS analysis proved to be a key recommendation that Berkeley’s Chief Resiliency Officer took to the city council for a bond measure to fund retrofits for their care and shelter sites. If Berkeley secures the funding for these retrofits, our analysis will have provided leverage for a policy directive that will result in increased protection for particularly vulnerable segments of the population exposed to seismic risk.

RMS was able to showcase the seismic risk of all neighborhoods throughout the city, contextualize the geographic vulnerability of shelter sites, and propose measures for helping to ensure that these critical pieces of infrastructure help to protect the populations that they serve. This project highlights that catastrophe modeling can be a key determinant in helping governments, NGOs, and the private sector understand their risk and increase resilience.

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.

Understanding the Principles of Earthquake Modeling from the 1999 Athens Earthquake Event

The 1999 Athens Earthquake occurred on September 7, 1999, registering a moment-magnitude of 6.0 (USGS). The tremor’s epicenter was located approximately 17km to the northwest of the city center. Its proximity to the Athens Metropolitan Area resulted in widespread structural damage.

More than 100 buildings including three major factories across the area collapsed. Overall, 143 people lost their lives and more than 2,000 were treated for injuries in what eventually became Greece’s deadliest natural disaster in almost half a century. In total the event caused total economic losses of $3.5 billion, while insured loss was $130 million (AXCO).

(USGS)

Losses from such events can often be difficult to predict; historical experience alone is inadequate to predict future losses. Earthquake models can assist in effectively managing this risk, but must take into account the unique features that the earthquake hazard presents, as the 1999 Athens Earthquake event highlights.

Background seismicity must be considered to capture all potential earthquake events

The 1999 event took Greek seismologists by surprise as it came from a previously unknown fault. Such events present a challenge to (re)insurers as they may not be aware of the risk to properties in the area, and have no historical basis for comparison. Effective earthquake models must not only incorporate events on known fault structures, but also capture the background seismicity. This allows potential events on unknown or complicated fault structures to be recorded, ensuring that the full spectrum of possible earthquake events is captured.

Hazard can vary greatly over a small geographical distance due to local site conditions

Soil type had significant implications in this event. Athens has grown tremendously with the expansion of the population into areas of poorer soil in the suburbs, with many industrial areas concentrated along the alluvial basins of the Kifissos and Ilisos rivers. This has increased the seismic hazard greatly with such soils amplifying the ground motions of an earthquake.

The non-uniform soil conditions across the Athens region resulted in an uneven distribution of severe damage in certain regions. The town of Adames in particular, located on the eastern side of the Kifissos river canyon, experienced unexpectedly heavy damage wheras other towns of equal distance to the epicenter, such as Kamatero, experienced slight damage. (Assimaki et al. 2005)

Earthquake models must take such site-specific effects into account in order to provide a local view of the hazard. In order to achieve this, high-resolution geotechnical data, including information on the soil type, is utilized to determine how ground motions are converted to ground shaking at a specific site, allowing for effective differentiation between risks on a location level basis.

Building properties have a large impact upon damageability

The 1999 Athens event resulted in the severe structural damage to, in some cases the partial or total collapse of, number of reinforced concrete frame structures. Most of these severely damaged structures were designed according to older seismic codes, only able to withstand significantly lower forces than those experienced during the earthquake. (Elenas, 2003)

A typical example of structural damage to a three-story residential reinforced-concrete building at about 8km from the epicentre on soft soil. (Tselentis and Zahradnik, 2000)

Earthquake models must account for such differences in building construction and age. Variations in local seismic codes and construction practices the vulnerability of structures can change greatly between different countries and regions, with it important to factor these geographical contrasts in. It is important for earthquake models to capture these geographical differences of building codes and this can be done through the regionalization of vulnerability.

Additionally, the Athens earthquake predominantly affected both low and middle rise buildings of two to four stories. The measured spectral acceleration (a unit describing the maximum acceleration of a building during an earthquake) decreased rapidly for buildings with five stories or more, indicating that this particular event did not affect high rise buildings severely. (Anastasiadis et al. 1999)

Spectral response based methodology most accurately estimates damage, modeling a building’s actual response to ground motions. This response is highly dependent upon building height. Due to the smaller natural period at which low and middle rise buildings oscillate or sway, they respond greater to higher frequency seismic waves such as those generated by the 1999 Athens event; while the reaction of high rise buildings is the opposite, responding the most to long period seismic waves.

The key features of the RMS Europe Earthquake Models ensure the accurate modeling of events such as the 1999 Athens Earthquake, providing a tool to effectively underwrite and manage earthquake risk across the breadth of Europe.