Many advances, but still unknowns in earthquake science
The great earthquake of 1933, estimated as a magnitude 6.4, killed 53 people in Long Beach out of 120 total fatalities across the region, destroyed or damaged 120 school buildings, devastated more than 1,800 homes and damaged tens of thousands more.
It led to landmark legislation enacted within 30 days -- the Field Act, named after Assemblyman Don C. Field, that has governed billions of dollars worth of planning, design and construction of public schools to make them more safe. That legislation led to further laws that have refined earthquake codes and building standards through the years that are still being developed and tweaked.
The Long Beach quake was also one of the early shakers to be monitored by motion sensing equipment in Vernon and Los Angeles, although it knocked the seismometer in Pasadena off its scale. Those early measurements gave scientists a true sense of the mechanics and effects of a hard shaking.
"It was really the beginning of the learning curve," said Thomas L. Holzer, engineering geologist for the U.S. Geological Survey in Menlo Park.
The Long Beach quake was also pivotal in the career of Charles Richter and helped cement his dedication to early seismology.
And yet, 80 years later, earthquakes in many ways remain scientifically among the great
mysteries of the globe. In an era of stunning and exponential advancements in science, geophysics to some seems to move at the same glacial pace as the Earth it studies. Others say the advances have been profound, if not generally noticed.Geologists and geophysicists still can't be sure exactly when, where, or in what magnitude quakes will strike. They cannot say which if any of the 10,000 small quakes measured each year in Southern California will trigger the cascade to "the big one."
They can't tell you with certainty, looking at two buildings side by side, which will ride out the shaker and which will collapse. Variables like soil and small architectural details can make all the difference.
Seismologists still can't account for all the "blind faults" that crisscross the region.
"A lot of faults are found because they cause quakes," said seismologist Susan Hough.
So confounding are quakes that the old wives' tales of "earthquake weather" and animal sensitivity persist and can't necessarily be discounted.
Holzer said because so much of what occurs with an earthquake happens beneath the surface at depths of 10 to 20 miles or deeper, scientists have a hard time understanding what is going on.
"It's difficult to see faults. We sort of have one hand tied behind our backs," he said. "If it erupts to the surface, we can see it and touch it. But for faults buried, it's hard to identify where it occurred."
Hough, who works for the US Geological Survey, said in some ways the complexity and variables in predicting weather and earthquakes are similar. The difference is one can observe cloud formations and movement that you can watch develop to make reasonable predictions about what will happen.
"Earthquakes are playing out deep underground, so it's complicated, and observations are limited," Hough said.
In an old geology joke, a geophysicist is asked what two times two equals, and the answer is, "How much do you want it to be?"
However, Hough will tell you the scientific advancements have been profound since the Long Beach quake and shouldn't be taken lightly.
"Seismology has completely transformed since then," she said. "There's been huge progress."
When the '33 quake happened, Charles Richter hadn't even published his famous eponymous scale.
Hough said the understanding of why quakes happen, their rates and predictions of magnitudes and types of shaking, the mapping of seismic hazard zones and the monitoring and precision of measurements has advanced significantly over the past century.
She also noted that in California, for example, seismological data has only been measured since 1932. And at that time, there was considerable debate about whether there were even active faults in Southern California.
The big riddle seismologists haven't been able to solve, the pi, if you will, of the science, has been the ability to accurately predict when major quakes will occur.
"In the '30s, (scientists) hoped if you could deploy enough monitors to determine patterns, but it has eluded us," Hough said. "People can get hung up on that."
What most often happens with earthquakes is that the learning happens after they hit.
The answers are usually the whys rather than the ifs.
The Long Beach quake was a shocking display of the inadequacy of unreinforced masonry. The Loma Prieta earthquake later showed the dangers of building on land-fill and mud. The Northridge quake of 1994 revealed the weakness of certain welds and brought into question the invincibility of steel in quakes.
"Each quake teaches us something," Holzer said.
And with each, new standards for construction and advances in understanding of infrastructure's abilities to withstand quakes are revealed.
The problem, according to Holzer, is that the infrequency of major quakes makes it easy for people to forget.
"The sun is out most days and we're not shaking," he said.
Meanwhile, the search for meaningful advance earthquake detection continues, with no certainty it will ever be found.
"Some scientists say it's impossible," said Hough, who calls herself an agnostic with regard to that question. "We really don't know what happens in the minutes and days before (an earthquake) happens. I don't think we can say (early prediction) can't happen. You never know what science will prove."
--
__._,_.___
No comments:
Post a Comment