Tag Archives: reconnaissance

Irma: From What Could Happen to What Did Happen…

17:00 UTC Tuesday, September 12

Emily Paterson, director – Model Product Management, RMS

Irma has now dissipated to the relief of many, not least those who experienced the storm’s wrath. The actuality of Irma was not nearly as bad as feared, as discussed in my colleague Tom Sabbatelli’s blog yesterday. Irma’s final path spared the major population centers of Miami and Tampa from the storm’s most damaging winds and storm surge.

Prior to and immediately after landfall, before we could see the final path and the actual impact of Irma, the best that anyone can do is look at the range of possible losses — as the final actual loss can only be known after an event is fully over and the details become clear.

To help our clients understand the potential magnitude of Irma’s insured loss during the storm’s approach, RMS provided guidance around what the distribution of potential wind losses looked like. But although we can have a good level of confidence in potential wind scenarios ahead of time, it is only part of the equation. As the hurricane approaches, we can provide guidance on the risk and identify areas that could be affected by storm surge and flooding, but the distribution of potential losses from these perils is uncertain as these losses are highly sensitive to the nuances of the storm’s final track and wind field structure.

Remember that the Saffir-Simpson scale no longer advises on the expected levels of storm surge following Hurricanes Katrina and Ike — storms that disproved the conventional understanding of the links between a hurricane’s intensity and its storm surge potential.

Now that Irma has gone, observations and imagery have started to come in that reveal the storm’s true impact. We are now able to shift our focus from “what could happen” to “what did happen”, from postulating potential wind loss distributions to delving into the hazard — including storm surge and flood — and damage observations to inform our final reconstructions of the event. Ultimately our understanding of the totality of losses from Irma will account for all loss drivers, including those which were too uncertain to estimate ahead of time. Storm surge, flood and other complicating factors, such as the evacuations, business interruption, and the prolonged and extensive power outages, among others, will all play a part in the final outcome.

While Irma has only dissipated very recently, what is already very clear is that Irma is a very complicated and complex event. How the interplay between wind, storm surge and flood plays out in terms of losses, and adding on top the impact of the complicating factors listed above, will ultimately dictate what the final losses will be.

Wind and surge observations from anemometers and gauges go a long way in helping us to better understand the hazard experienced on the ground, and are crucial as we look to reconstruct the hazard from Irma – our first step to understanding the full loss.

Satellite and drone imagery helps us go one step further and gives us a “birds eye view” of the damage experienced, helping to provide a fuller picture of both the type and level of damage, as well as a good indication of the extent. As we inspect the imagery we are looking for things that will help us refine our understanding of losses from this event — how far inland can we see surge damage? Is there roof damage from winds over a large area? We can use these observations to help refine and validate our understanding of loss. Another advantage of leveraging imagery is that it helps inform where we should focus our field reconnaissance efforts.

Figure 1. Map showing Key West Naval Base with photo image of residential area in the top right corner.  Source: OpenStreetMap

Figure 2: Residential area near Key West Naval Base, pre-event image from Google Earth, post-event aerial image acquired by NOAA on September 11, 2017

Our “boots on the ground” field reconnaissance approach really helps us refine our understanding with more detailed information. Not only does it help validate hazard observations with damage observations, but conversations with home and business owners, as well as those working on the recovery efforts, gives us insight into the prolonged effects impacting the affected communities, such as lengthy closures of businesses and insight into the types of internal and contents damage experienced by homeowners.  Our field reconnaissance plans are already underway and as those field observations come in, they will be fed into our process as well. The more information we have about the damage on the ground, the better our understanding of the full totality of losses from an event will be.

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.