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Impearls: 2003-05-04 Archive

Earthdate 2003-05-08

Earthquakes in Developed Countries

USGS: earthquake distribution in the U.S. map, 1989

Historical earthquake distribution across the United States
(click on image for larger scale)

Jay Manifold in an article “Earthquakes and Economies” in A Voyage To Arcturus writes:

The recent strong, shallow earthquake in Turkey brought to mind a longstanding risk-management concern of mine: how to prevent high casualties from such events in the Third World?  Over on EurekAlert, we find Growing world urban populations threatened by massive earthquakes; key quotes:

[University of Colorado at Boulder geological sciences professor Roger] Bilham said a “fractal distribution of fatality count versus the number of fatal earthquakes permits a grim glimpse of possible future earthquake disasters based on past events.”

… recent research by Bilham and his colleagues indicate that at least one and perhaps as many as seven 8.1 magnitude to 8.3 magnitude earthquakes are overdue in the Himalayas facing northern India.

Bilham believes there is room for optimism, though he characterizes the present era as the age of construction when 3 billion new dwellings presently are being planned for a future doubling of the world population.  “We are in a remarkably good position to make these new buildings safe to live in,” he said.

“Earthquakes don't kill people, but buildings and builders of inferior buildings do.”

A key insight; compare the death tolls from Loma Prieta with those of Kobe, two events of nearly identical magnitude and depth.  But one killed over 5,000, and the other killed 63.

Bilham's reasoning should be extended.  Why are inferior buildings constructed?  What conditions foster improvement in building construction — what mores, what institutions, what public policies?  The contrasts between Japan and the US, let alone between Turkey and the US, strongly suggest that open societies with competitive economic systems and a commitment to preventing corruption and protecting individuals — in other words, where markets and the rule of law prevail — are the ultimate lifesaver.

I agree in principle with the point Jay is making (indeed, I used to agree almost completely with his position), but I've come to see that the idea has major difficulties in practice, at least in short- to medium-term practice.  To be sure, Jay's expressed view has some truth in it.  Earthquakes such as the one in 1976 in T'ang-shan, China, which killed more than 240,000 people, or the 1988 quake in Armenia with a death toll of 25,000, clearly show I think the unfortunate effect that large-scale use of unreinforced masonry and concrete construction has in earthquake country.

Jay relates predicted magnitude 8.1 to 8.3 earthquakes expected in India in the future to death tolls from two recent magnitude 7.1 quakes in the U.S. and Japan.  However, magnitude 7.x and 8.x earthquakes, measured on the (logarithmic) Richter scale, are really two quite different beasts, operating on almost wholly different scales of violence.  Earthquakes of magnitude 7.1, as in the 1989 Loma Prieta earthquake in California (the so-called “World Series” quake) and similar magnitude 1995 quake in Kobe, Japan (the examples that Jay presents) — while quite severe earthquakes in their own right — produce only one-tenth of the amount of ground shaking and one-thirtieth the energy released by an 8.1 magnitude quake.  (Magnitude 8.1 and above quakes known previously in the U.S. include the huge 1857 Los Angeles and 1906 San Francisco earthquakes, the tremendous 1964 Alaska quake, and three massive earthquakes over a period of two months during 1811-12 in what is now the state of Missouri.)

As a result of the extreme difference in scale between 7.x and 8.x magnitude quakes, many human structures which could withstand a 7.1 earthquake with little damage would be completely flattened by 8.1 and larger quakes.  The latter far more violent earthquakes not only take place with much less frequency, but those that have occurred during recent, highly technological times have been poorly instrumented with sensors, so that little experience exists on details of the shaking and even less on what improved construction techniques are needed to withstand such giant quakes.  Certainly zoning requirements and building construction codes haven't caught up (even in quake heavy regions like California and Japan) with what's needed to cope with these super-quakes — and, as I say, we don't even know yet what's really required to resist them.

Even with regard to the relatively “puny” magnitude 7.x earthquakes that we have a fair amount of experience with, however, the situation turns out not to be sanguine.  Jay might have noticed a clue that something's lacking in his analysis from the fact that the Kobe earthquake to which he refers occurred in Japan: hardly an underdeveloped country, nor are devastating earthquakes at all rare in that land.  I'm not familiar with Japanese building codes, but I seriously doubt they're much if any inferior with regard to earthquake resistance than are California's codes (much less the practically non-existent earthquake codes across the rest of the U.S.: areas which are expected to “never” see earthquakes — places like, say, Missouri!).

The reason quakes appear far less deadly in America than even in advanced places in Asia such as Japan derives partly from the fact that earthquakes are rare across much of the United States, and America's history is short.  Beyond that, the U.S. is vast and (even with a population in the hundreds of millions) is mostly quite sparsely populated, especially in the west where, for geological reasons, most earthquakes take place.  Even California, the most populous state in the Union, is largely empty: three quarters of the population reside within the San Francisco, Los Angeles, and San Diego metropolitan areas.  Thus, earthquakes are much more likely to occur in the U.S. in places where there are relatively few people.  Unfortunately, as San Francisco discovered in 1906 (particularly as in the case of the most massive quakes, several hundred miles of fault break at once), one can't rely on that kind of protection forever.

The Loma Prieta earthquake killed so few people relative to the similar magnitude Kobe quake not only due to its remote location — the Santa Cruz Mountains of California — but because in addition to its remoteness most of the relatively sparse population live in wood-frame homes which are very effective in resisting catastrophic damage from earthquakes.  Even so, a number of homes closely adjacent to the slipping portion of the San Andreas Rift fell flat that day.  Reportedly, accelerations from the Loma Prieta quake in the immediate vicinity of the San Andreas equaled earth's gravity but in a horizontal direction!  It's hard for most any home or structure to resist that.

Nine miles from the epicenter, the downtown business district of the nearby city of Santa Cruz was heavily damaged.  Beyond those local areas, however, most of the devastation resulting from Loma Prieta occurred over 60 miles away, in ground-fill regions of the cities of San Francisco and Oakland — areas highly susceptible to “liquefaction.”  As the U.S. Geological Survey has pointed out, had an earthquake of similar magnitude occurred beneath the latter heavily populated areas, damage and deaths would have been far more severe.  A USGS publication “The Loma Prieta Earthquake of October 17, 1989,” published shortly after the Loma Prieta quake, predicts the following in this regard: 1

The Loma Prieta earthquake was one of the costliest natural disasters in U.S. history.  The earthquake occurred in the remote Santa Cruz Mountains and caused severe damage in San Francisco and Oakland, 50 miles north of the end of the fault segment that slipped.

  • Deaths: 62
  • Injuries: 3,757
  • Damage: more than $6 billion
  • San Francisco Bay bridge unusable for 1 month
  • Number of homes damaged: 18,306
  • Number of business damaged: 2,575
  • Persons displaced: 12,053

BUT… What will happen when an earthquake of similar magnitude occurs close to these population centers?

An earthquake of magnitude 7.5 on the eastern Bay Area's Hayward fault […], for example, is likely to be far more destructive than the Loma Prieta event.  An “Earthquake Planning Scenario” developed by the California Division of Mines and Geology […] and “An Assessment of the Consequences and Preparations for a Catastrophic California Earthquake” by the Federal Emergency Management Agency […] anticipate the following effects:

  • Deaths: 1,500 - 4,500
  • Injuries: 45,000 - 135,000
  • Damage: More than $40 billion
  • One or more hospitals will be destroyed
  • All four bridges to the East Bay will probably be closed for hours to days
  • Access to and travel within the East Bay will be difficult and limited to emergency traffic.
  • Only San Jose International Airport may be available for large aircraft.
  • The damage in San Francisco is likely to be severe — the Embarcadero area is as close to the Hayward fault as it is to the San Andreas fault.

Notice how closely the USGS's prediction for a future 7.x magnitude earthquake in the San Francisco Bay Area tracks the actual death toll from the subsequent similar-magnitude earthquake at Kobe, Japan (more than 5,000 dead).

Which raises the vital question: given the present strong earthquake construction codes that both California (though not much of the rest of the U.S.) and Japan have painfully, incrementally after each earthquake disaster, put together, why aren't we in the developed world (or at least in places like California and Japan) better protected against future earthquakes even on the relatively modest scale of the Loma Prieta and Kobe quakes?  (Not to speak of a future 8.x magnitude “Big One”….)

The answer is clear: for practical and political reasons, earthquake codes are never made retroactive.  While I sympathize with the plight of building owners who face a tremendous burden in upgrading those structures, the fact remains that there continue to exist in modern California, after more than 150 years of sizable earthquakes, tens of thousands of unreinforced masonry and concrete structures: multistory buildings similar basically to the double-decker “Cypress-structure” freeway in Oakland that pancaked during the Loma Prieta quake squashing dozens of motorists, but spanning three dimensions rather than one and full of people.

Unfortunately, I expect this situation will not change in the foreseeable future, and those highly vulnerable buildings will only be “upgraded,” so to speak, when they're eventually knocked down by earthquakes, with extensive loss of life.

Note that even areas in America which haven't seen large earthquakes since the European settlement aren't really safe: it's rather that the longer time scale for sizable quakes to occur in those regions of the country hasn't yet elapsed (see the map below).  So, while as a Californian I admire the beauty of the striking brick buildings sprawling in large numbers across the eastern half of North America, my next thought, however, whenever I see them is deathtrap.

UPDATE:  2003-05-12 12:00 UT:  Changed a few words in the foregoing to improve clarity and made minor corrections to fact (e.g, the distance from the Loma Prieta quake's epicenter to Santa Cruz and San Francisco/Oakland); also added a paragraph to the quote from Jay Manifold's piece that I'd intended to include but hadn't.

Meanwhile, Jay has posted a reply in A Voyage To Arcturus to my article.  Jay disagrees with my conclusion (which he correctly summarizes as “earthquakes with Kobe-class body counts are still a possibility for the US”), continuing to believe that the higher death tolls due to earthquakes in places like Japan are a result of institutional and cultural differences rather than, basically, luck.  I'd originally included a response to his reply under this Update, but since I kept revising and adding to it, I've now split it off into a separate posting.

UPDATE:  2005-10-15 15:40 UT:  Changed hosting and reduced compression on map images.  The displayed map is now larger.  Unfortunately, due to host image dimension limits, the linked-to map is now smaller.  Moved maps to top of article.


1 Peter L. Ward and Robert A. Page, “The Loma Prieta Earthquake of October 17, 1989,” U.S. Geological Survey publication, November 1989; pp. 7 and 16 (map).


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