Monthly Archives: May 2015

“San Andreas” – The Scientific Reality

San Andreas—a Hollywood action-adventure film set in California amid not one, but two magnitude 9+ earthquakes in quick succession and the destruction that follows—was released worldwide today. As the movie trailers made clear, this spectacle is meant to be a blockbuster: death-defying heroics, eye-popping explosions, and a sentimental father-daughter relationship. What the movie doesn’t have is a basis in scientific reality.

Are magnitude 9+ earthquakes possible on the San Andreas Fault?

Thanks to the recent publication of the third Uniform California Earthquake Rupture Forecast (UCERF3), which represents the latest model from the Working Group on California Earthquake Probabilities, an answer is readily available: no. The consensus among earth scientists is that the largest magnitude events expected on the San Andreas Fault system are around M8.3, forecast in UCERF3 to occur less frequently than about once every 1 million years. To put this in context, an asteroid with a diameter of 1,000 meters is expected to strike the Earth about once every 440,000 years. Magnitude 9+ earthquakes on the San Andreas are essentially impossible because the crustal fault zone isn’t long or deep enough to accumulate and release such enormous levels of energy.

My colleague Delphine Fitzenz, an earthquake scientist, in her work exploring UCERF3, has found that, ironically, the largest loss-causing event in California isn’t even on the San Andreas Fault, which passes about 50 km east of Los Angeles. Instead, the largest loss-causing event in California is one that spans the Elsinore Fault and runs up one of the blind thrusts, like the Compton or Puente Hills faults, that cuts directly below Los Angeles. But the title Elsinore + Puente Hills doesn’t evoke fear to the same degree as San Andreas.

Will skyscrapers disintegrate and topple over from very strong shaking?

Source: San Andreas Official Trailer 2

Short answer: No.

In a major California earthquake, some older buildings, such as those made of non-ductile reinforced concrete, that weren’t designed to modern building codes and that haven’t been retrofitted might collapse and many buildings (even newer ones) would be significantly damaged. But buildings would not disintegrate and topple over in the dramatic and sensational fashion seen in the movie trailers. California has one of the world’s strictest seismic building codes, with the first version published in the early part of the 20th century following the 1925 Santa Barbara Earthquake. The trailers’ collapse scenes are good examples of what happens when Hollywood drinks too much coffee.

A character played by Paul Giamatti says that people will feel shaking on the East Coast of the U.S. Is this possible?

First off, why is the movie’s scientist played by a goofy Paul Giamatti while the search-and-rescue character is played by the muscle-ridden actor Dwayne “The Rock” Johnson? I know earth scientists. A whole pack of them sit not far from my desk, and I promise you that besides big brains, these people have panache.

As to the question: even if we pretend that a M9+ earthquake were to occur in California, the shaking would not be felt on the East Coast, more than 4000 km away. California’s geologic features are such that they attenuate earthquake shaking over short distances. For example, the 1906 M7.8 San Francisco Earthquake, which ruptured 477 km of the San Andreas Fault, was only felt as far east as central Nevada.

Do earthquakes cause enormous cracks in the earth’s surface? 

Source: San Andreas Official Trailer 2

I think my colleague Emel Seyhan, a geotechnical engineer who specializes in engineering seismology, summed it up well when she described this crater from a trailer as “too long, too wide, and too deep” to be caused by an earthquake on the San Andreas Fault and like nothing she had ever seen in nature. San Andreas is a strike-slip fault; so shearing forces cause slip during an earthquake. One side of the fault grinds horizontally past the other side. But in this photo, the two sides have pulled apart, as if the Earth’s crust were in a tug-of-war and one side had just lost. This type of ground failure, where the cracks open at the surface, has been observed in earthquakes but is shallow and often due to the complexity of the fault system underneath. The magnitude of the ground failure in real instances, while impressive, is much less dramatic and typically less than a few meters wide. Tamer images would not have been so good for ticket sales.

Will a San Andreas earthquake cause a tsunami to strike San Francisco?

Source: San Andreas Official Trailer 2

San Andreas is a strike-slip fault, and the horizontal motion of these fault systems does not produce large tsunami. Instead, most destructive tsunami are generated by offshore subduction zones that displace huge amounts of water as a result of deformation of the sea floor when they rupture. That said, tsunami have been observed along California’s coast, triggered mostly by distant earthquakes and limited to a few meters or less. For example, the 2011 M9 Tohoku, Japan, earthquake was strong enough to generate tsunami waves that caused one death and more than $100 million in damages to 27 harbors statewide.

One of the largest tsunami threats to California’s northern coastline is from the Cascadia Subduction Zone, stretching from Cape Mendocino in northern California to Vancouver Island in British Colombia. In 1700, a massive Cascadia quake likely caused a 50-foot tsunami in parts of northern California, and scientists believe that the fault has produced 19 earthquakes in the 8.7-9.2 magnitude range over the past 10,000 years. Because Cascadia is just offshore California, many residents would have little warning time to evacuate.

I hope San Andreas prompts some viewers in earthquake-prone regions to take steps to prepare themselves, their families, and their communities for disasters. It wouldn’t be the first time that cinema has spurred social action. But any positive impact will likely be tempered because the movie’s producers played so fast and loose with reality. Viewers will figure this out. I wonder how much more powerful the movie would have been had it been based on a more realistic earthquake scenario, like the M7.8 rupture along the southernmost section of the San Andreas Fault developed for the Great Southern California ShakeOut. Were such an earthquake to occur, RMS estimates that it would cause close to 2,000 fatalities and some $150 billion in direct damage, as well as significant disruption due to fault offsets and secondary perils, including fire following, liquefaction, and landslide impacts. Now that’s truly frightening and should motivate Californians to prepare.

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.

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.”

 

An Industry Call to Action: It’s Time for India’s Insurance Community To Embrace Earthquake Modeling

The devastating Nepal earthquake on April 25, 2015 is a somber reminder that other parts of this region are highly vulnerable to earthquakes.

India, in particular, stands to lose much in the event of an earthquake or other natural disaster: the economy is thriving; most of its buildings aren’t equipped to withstand an earthquake; the region is seismically active, and the continent is home to 1.2 billion people—a sizeable chunk of the world’s population.

In contrast to other seismically active countries such as the United States, Chile, Japan and Mexico, there are few (re)insurers in India using earthquake models to manage their risk, possibly due to the country’s nascent non-life insurance industry.

Let’s hope that the Nepal earthquake will prompt India’s insurance community to embrace catastrophe modeling to help understand, evaluate, and manage its own earthquake risk. Consider just a few of the following facts:

  • Exposure Growth: By 2016, India is projected to be the world’s fastest growing economy. In the past decade, the country has experienced tremendous urban expansion and rapid development, particularly in mega-cities like Mumbai and Delhi.
  • Buildings are at Risk: Most buildings in India are old and aren’t seismically reinforced. These buildings aren’t expected to withstand the next major earthquake. While many newer buildings have been built to higher seismic design standards they are still expected to sustain damage in a large event.
  • Non-Life Insurance Penetration Is Low but Growing: India’s non-life insurance penetration is under one percent but it’s slowly increasing—making it important for (re)insurers to understand the earthquake hazard landscape.

Delhi and Mumbai – Two Vulnerable Cities

India’s two mega cities, Delhi and Mumbai, have enjoyed strong economic activity in recent years, helping to quadruple the country’s GDP between 2001 and 2013.

Both cities are located in moderate to high seismic zones, and have dense commercial centers with very high concentrations of industrial and commercial properties, including a mix of old and new buildings built to varying building standards.

According to AXCO, an insurance information services company, 95 percent of industrial and commercial property policies in India carry earthquake cover. This means that (re)insurers need to have a good understanding of the exposure vulnerability to effectively manage their earthquake portfolio aggregations and write profitable business, particularly in high hazard zones.

For (re)insurers to effectively manage the risk in their portfolio, they require an understanding of how damage can vary depending on the different type of construction. One way to do this is by using earthquake models, which take account of the different quality and types of building stock, enabling companies to understand potential uncertainty associated with varying construction types.

A Picture of India’s Earthquake Risk

India sits in a seismically active region and is prone to some of the world’s most damaging continental earthquakes.

The country is tectonically diverse and broadly characterized by two distinct seismic hazard regions: high hazard along the Himalayan belt as well as along Gujarat near the Pakistan border (inter-plate seismicity), and low-to-moderate hazard in the remaining 70 percent of India’s land area, known as the Stable Continental Region.

The M7.8 Nepal earthquake occurred on the Himalayan belt, where most of India’s earthquakes occur, including four great earthquakes (M > 8). However, since exposure concentrations and insurance penetration in these areas are low, the impact to the insurance industry has so far been negligible.

In contrast, further south on the peninsula where highly populated cities are located there have been several low magnitude earthquakes that have caused extensive damages and significant casualties, such as the Koyna (1967), Latur (1993), and Jabalpur (1997) earthquakes.

It is these types of damaging events that will be of significance to (re)insurers, particularly as insurance penetration increases. Earthquake models can help (re)insurers to quantify the impacts of potential events on their portfolios.

Using Catastrophe Models to Manage Earthquake Risk

There are many tools available to India’s insurance community to manage and mitigate earthquake risk.

Catastrophe models are one example.

Our fully probabilistic India Earthquake Model includes 14 historical events, such as the 2001 Gurajat and 2005 Kashmir earthquakes, and a stochastic event set of more than 40,000 earthquake scenarios that have the potential to impact India, providing a comprehensive view of earthquake risk India.

Since its release in 2006, (re)insurers in India and around the world have been using the RMS model output to manage their earthquake portfolio aggregations, optimizing their underwriting and capital management processes. We also help companies without the infrastructure to use fully probabilistic models to reap the benefits of the model through our consulting services.

What are some of the challenges to embracing modeling in parts of the world like India and Nepal? Feel free to ask questions or comment below.