Author Archives: Callum Higgins

About Callum Higgins

Senior Product Analyst, Model Product Management

Based in London, Callum works within the Model Product Management team at RMS, focusing on the Australasia climate suite of products. As product manager for the Australia Cyclone and Severe Convective Storm models, Callum works with the RMS client facing and model development teams to translate market needs into model improvements and provides subject matter support for these models. He joined RMS in 2014 and prior to his current role supported a variety of models within the Model Product Management team through both technical analyses and the creation of product marketing materials and documentation. Callum holds an integrated master’s degree (MEarthSci) in Earth Sciences from Oxford University.

Severe Tropical Cyclone Debbie: Insights Resulting from RMS Support of the SWIRLnet Project

In what was an otherwise relatively quiet Australian cyclone season, Cyclone Debbie proved to be the exception, being the only severe tropical cyclone to make landfall. Although devastating for those affected, Debbie provided an opportunity to help better understand cyclones in the region and the damage they cause.

The Cyclone Testing Station at James Cook University (with collaborators from the Wind Research Laboratory at the University of Queensland) were able to deploy portable weather stations in advance of the event as part of its SWIRLnet (Surface Weather Relay and Logging Network) project, of which RMS is a benefactor.

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The 2016-17 Australian Cyclone Season: A Late Bloomer

The 2016-17 Australian region cyclone season will be remembered primarily as an exceptionally slow starter that eventually went on to produce a slightly below-average season in terms of activity.

With the official season running from November 1 to April 30 each year, an average of ten cyclones typically develop over Australian waters with around six making landfall, and on average, the first cyclone landfall is by December 25. For the 2016-17 season, we saw nine tropical cyclones, of which three further intensified into severe tropical cyclones and three of which made landfall, running contrary to an average to above-average forecast from the Bureau of Meteorology. Continue reading

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.

The 1960 Tele-tsunami: Don’t forget the far field

On May 22, 1960 the most powerful earthquake ever recorded struck approximately 100 miles off the coast of southern Chile. The 9.5 Mw event released the energy equivalent to 2.67 gigatones of TNT (178,000 times the energy yielded from the atomic bomb dropped on Hiroshima) leading to extreme ground shaking in cities such as Valdivia and Puerto Montt, triggering landslides and rockfalls in the Andes as well as resulting in a Pacific basin wide tsunami. In Chile, 58,622 houses were completely destroyed with damages totalling $550 million (~$4 billion today adjusted for inflation).

However, the effects in the far field were also significant. While the majority of the damage and approximately 1,380 fatalities occurred in close proximity to the earthquake, a proportion of the tsunami death toll and damage occurred over 5,000 miles away from the epicentre and reached as far away as Japan and the Philippines.

Such tsunamis with the potential to cause damage and fatalities at locations distant from their source are known as tele-tsunamis or far-field tsunamis and require a large magnitude earthquake (>7.5) on a subduction zone to be triggered. Recent events, such as the 2011 Tohoku and 2010 Maule earthquakes, demonstrated that even if these criteria are met, the effects of any resulting tsunami may not be felt significantly beyond the immediate coastline. As such, it can be easy to forget the risks at potential far field sites. However, the 55th anniversary of the 1960 Chilean earthquake and tsunami provides a useful reminder that megathrust earthquakes can have far reaching consequences.

Across the Pacific, the 1960 tsunami caused 61 deaths and $75 million damage (~$600 million today) in Hawaii, 138 deaths and $50 million damage (~$400 million today) in Japan, and left 32 dead or missing in the Philippines.

Hilo Bay, on the big island of Hawaii, was particularly hard hit with wave heights reaching 35 feet (~11 meters), compared to only 3-17 feet or 1-5 meters elsewhere in Hawaii. Approximately 540 homes and businesses were destroyed or severely damaged, wiping out much of downtown Hilo.

Hilo aftermath copy   hilo tsunami copy
                          Aftermath of the event in Hilo (USGS)                                               Inundation extent of the 1960 tsunami in Hilo (USGS)

Despite an official warning from the U.S. Coast and Geodetic Survey and the sounding of coastal sirens, 61 people in Hilo died as a result of the tsunami and an additional 282 were badly injured. The majority of these casualties occurred because people did not evacuate, either due to misunderstanding or not taking the warnings seriously. Many remained in the Waiakea peninsula area, which was perceived to be safe due to the minimal damage experienced there during the event triggered by the 1946 Aleutian Islands earthquake.

Others initially evacuated to higher ground but returned before the event had finished. A series of waves is a common feature of far field tsunamis, with the first wave typically not being the largest. This was the case with the 1960 event with a series of 8 waves striking Hawaii. Thethird of these was most damaging, killing many of those who returned prematurely.

These avoidable casualties highlight the need for adequate tsunami mitigation measures, including education to ensure that people understand the warnings and the correct actions to take in the event of a tsunami. This is particularly important in areas exposed to far field tsunami hazard, where people may be less aware of the risk and there is enough time to evacuate. The introduction of a Pacific Tsunami Warning System in 1968 as a consequence of the event was a big step forward in improving such measures, the presence of which would no doubt substantially reduce the death toll were the event to reoccur today.

Mitigation efforts can also be supported by tools like the RMS Global Tsunami Scenario Catalog, which provides information on the inundation extent and maximum inundation depth for numerous potential tsunami scenarios around the globe. This can be used to identify areas at risk to far-field tsunami events, including those with no historical precedent, enabling the quantification of exposures likely to be worst impacted by such events.