--Seize the Opportunity to Further Seismic Understanding: Earthquake Insight from Recent Study--
In 1960, the Earth rang, its crust shaken by the free oscillations of the world’s largest earthquake. One hundred twenty-three years of accumulated stress had come to call at a fault zone in south-central Chile, stirring the Earth and shocking seismologists; this giant quake had been early. Or had it?
The last known earthquake along the Chilean fault had struck in 1837, one hundred twenty-three years prior to 1960. Because an earthquake’s magnitude is generally thought to relate to the number of years between its occurrence and that of its predecessor, seismologists observing this span were perplexed. Sure, 123 years might sound like plenty of time for giant quake-causing stress to build in Earth’s outer layer, but historic record shows that typically, several centuries are required to build the type of energy this Chilean giant had rleased. One hundred plus years could hardly account for the energy with which this 1960 quake- literally off the Richter scale - had subducted the Nazca plate below its easterly neighbor (the South American plate), nor could this stunted span explain why associated tsunamis, or earthquake-generated waves, had soaked not only Chile, but Hawaii, Japan, and the Philippines, too.
Indeed, according to history, seismologists of 1960 should have felt safe assuring local south-central Chileans that a massive quake would not manifest itself there in the mid-twentieth century. But such a quake had. Futhermore, the entire timeline of quake activity at this fault zone confused seismologists; after the first documented earthquake there, observed by Spanish conquistadors in 1575, the zone was twice more shaken before 1960: in 1737, and again, exactly one-hundred years later, in 1837. So how to correlate this 1960 giant with such an earthquake history, showing a predecessor only a century or so before?
To explain this seismic mystery, Marco Cisternas, a Chilean researcher from the Pontificia Universidad Catolica de Valparaiso, joined ranks with a University of Washington geologist, Brian Atwater. As outlined in September 15th's "Nature," the two scientists and their colleagues sought to understand the 1960 earthquake based on physical evidence: shoreline changes in the stratigraphic record - in the sand and soil deposits produced by tsunamis.
At an estuary near the fault zone, Cisternas and Atwater investigated shoreline changes. Residents who witnessed the 1960 quake confirmed that the giant had indeed changed their shore: the green forest thriving there before, for example, was defoliated after the quake as a result of the tides that routinely flooded the subsided region following 1960. By contrast, nautical records depict leafy trees in this area after 1837. Why hadn’t 1837’s earthquake destroyed forests, too?
Examination of tsunami-generated sand deposition in this estuarine region provided further insight. Cisternas and Atwater observed that while both the 1575 and 1960 earthquakes were clear in the stratigraphic record, having covered marsh and meadow with up to 2 feet of sand, stratigraphic analysis pointed to no such significant sand deposition in layers associated with the quakes of 1737 and 1837.
Cisternas and Atwater concluded that, though tsunamis were indeed associated with these last two earthquakes, they were not nearly as sizeable as the earthquake-generated waves of 1575 and 1960, nor did their associated quakes expend much of the accumulated stress at the fault. The scientists propose that the earthquakes of 1737 and 1837 shook the earth on a much smaller scale than their sixteenth century predecessor, making 1575 the quake from which we should base history of 1960’s giant. In other words, massive fault dislocation from that earthquake was produced by energy that had remained “locked in” since 1575.
This 385 year gap fits the timeline for large earthquake recurrence. Additionally, Cisternas and Atwater’s study provides a wake-up call to seismologists content to consult history for earthquake understanding. No longer can it be assumed that the shaking of one quake stifles the same region from shaking again soon. Rather, giant earthquakes can still occur, even if mediocre ones have not-so-long-ago set the Earth ringing in the very same spot.
.MGW.
--Gender Mentor Makes us Wonder--
The Y chromosome is reporting to work early. With the release of last month’s Baby Gender Mentor Home DNA Gender Testing Kit, the presence of Y chromosome DNA has been employed to reveal fetal sex in record time: just 5 weeks after conception.
This test outpaces present methods of sex determination by a long shot; chorionic villus sampling and amniocentecis do not reveal male or female status until weeks 10 and 15, respectively. Both tests are used predominantly to screen for chromosomal abnormalities like Down syndrome, or for genetic defects, such as cystic fibrosis and Tay-Sachs disease. These tests also reveal fetal sex in this process. The Gender Mentor test, on the other hand, was specifically designed to reveal a baby’s sex.
This kit is for ''the type of woman who can't wait to open Christmas presents," says Sherry Bonelli, president of Mommy's Thinkin', the company that designed Gender Mentor. Indeed, as Bonelli intended, eager parents-to-be can now quench their curiousity and paint the nursery pink (or blue) with plenty of time to spare. And they don’t need to consult a physician to gain this knowledge of sex; Bonelli’s genetic test is directly marketed to consumers. Offered outside the usual context of medical consulation, it can be purchased online for $25. Acu-Gen Labs in Lowell, Massachusetts, charges $250 more for processing, for a grand total of 275$.
How does this test actually work? Lab tests analyze the fetal DNA floating in a finger-prick sample of a pregnant woman’s blood. (A finger-prick blood sampling kit is included in the Gender Mentor package.) Because human DNA is so similar from person to person, the best way to distinguish fetal DNA from maternal DNA is if there is Y chromosome in the sample- that is, if the fetus is a boy. Thus, Acu-Gen tests for the presence of Y chromosome DNA. A woman whose blood sample shows it can expect a boy. Likewise, absence of Y chromosome DNA in a pregnant woman means that a girl is on the way.
C.N. Wang, scientific director of Mommy’s Thinkin’, reports that Gender Mentor is designed to showcase the power of a new DNA analysis technique that holds promise for serious clinical uses, from early cancer testing to prenatal diagnosis of Down syndrome. These are the applications to which most scienctists are directing their attention. Free-cell DNA associated with tumors, for example, could make blood tests standard for detection in cancer patients, who would otherwise require chemotherapy. At this stage, however, the test is not used as a diagnostic tool.
Bioethicists are concerned about implications of Gender Mentor. They worry that this product will be used as a means for selecting sex, inciting couples unhappy with the determined sex to abort. Arthur Caplan, chairman of the department of medical ethics at the University of Pennsylvania, warns that being only five weeks into a pregnancy changes the moral view for people. “Ending a pregnancy early is easier to do [at 5 weeks] than at 20 weeks,“ Caplan said.
Previously, procedures like CVS and amniocentesis have escaped this concern; they are powerless to determine fetal sex until later stages when a) most mothers-to-be have already chosen to continue their pregnancies and b) the State becomes legally interested in the viability of the fetus.
But Bonelli claims that sex-selection via abortion is a non-issue in the United States. Here, she says, there are no dowries or other other culturally specific influences which fuel the boy preference prevalent in places like China and India.
However, despite Bonelli’s claims, sex selection is not absent from reproductive clinics in America. At the Genetics and IVF Institute in Fairfax, Virginia, a technology called MicroSort, which separates sperm into X and Y specimen based on weight, is part of the current commercial effort to standardize sex selection. The Virginia-based clinic has received 1,300 requests for MircroSort procedures since it opened in 1995. The Micrsort technique costs 5000 dollars per sitting compared to Gender Mentor’s 275 (kit + lab test). Incidentally, it appears that sex-selection in the United States is becoming a profitable industry. And why are Americans taking part?
One reason reported: to achieve “balanced” families – families with equal (or close to equal) numbers of boys and girls. In 2000, the Scottish couple Lousie and Alan Masterton made international headlines in their fight with the Human Fertilzation and Embryology Authority. They saught to “balance their family" by selecting for a girl to replace a lost daugter, Nicole. "We are missing the female element," said Louise Masterton, mother of 4 boys. The HFEA denied the Masterton’s requests, however, holding fast to the creed that sex-selction should be reserved for medical purposes, such as avoiding sex-linked diseases.
Beyond family balancing, Microsort reports that Americans are also seeking to sex-select to control gender order. Couples may want to raise a boy first, and then bring the girl home. A nation of little sisters in the making?
Though sex selection may or may not become widespread in the U.S., the idea of a direct-to-consumer genetic test like Gender Mentor does raise questions. In a report from the Human Genetics Commission, chairman Philip Webb addresses the role of this technology in America: “Genetic testing will become much more prevalent in future and has the potential to deliver significant health benefits,” he claims, “but it is important that direct testing is now somewhat regulated in such a way that we can gain the benefits of our new knowledge.” Webb’s statement serves as a reminder that genetic technology is progressing on a fast track, along which Americans may or may not be regulated. The option provided by Gender Mentor- to determine fetal sex as early as 5 weeks- poses to parents the question of whether knowledge of a child’s sex so soon after conception would be beneficial. Gender Mentor could make such knowledge readily available. But who will mentor minds struggling to answer this question?
.MGW.
