I read this article a few years ago and it keeps poping up.

SMU RESEARCHERS DESCRIBE TWO SEISMIC EVENTS WITH THE PROPERTIES FOR THE PASSAGE OF STRANGE QUARK MATTER THROUGH THE EARTH

DALLAS (SMUNews) — Researchers from Southern Methodist University have described two seismic events that they believe may offer the first evidence of a previously undetected form of matter passing through the earth.

This form of matter — known as “strange quark matter” — is so dense that a ton-sized nugget would be about the size of a red blood cell. Physicists have suspected since 1984 that this very heavy form of matter might exist, but no one has yet found evidence of it.

In 1984, Harvard physicist and Nobel Laureate Sheldon L. Glashow suggested that one way such matter might be found would be if a physicist teamed up with a seismologist to search for traces of the matter that might have passed through the earth at supersonic speed. In 1993, SMU physicist Vidgor Teplitz asked Eugene Herrin, a seismologist in the Department of Geological Sciences in SMU’s Dedman College, to collaborate with him on the project. The two were assisted by David Anderson, a senior systems analyst in the Department of Geological Sciences, and Ileana Tibuleac, then a Ph.D. student in the Department of Geological Sciences.

In a paper submitted to the Bulletin of the Seismological Society of America and published online at http://xxx.lanl.gov/ (subject area: astrophysics), the SMU researchers describe how they found evidence of strange quark matter by searching through more than a million records of seismic events collected by the U.S. Geological Survey from 1990 to 1993 that were not associated with traditional seismic events such as earthquakes. These records of so-called “unassociated events” were collected from seismic stations set up around the world to monitor earthquakes and nuclear testing.

In a paper previously published in 1995 (available online at http://cornell.mirror.aps.org/abstract/PRD/v53/i12/p6762_1), Herrin and Teplitz had determined that it would be feasible to search for seismic events that might indicate passage of strange quark matter (also known as nuclearites) through the earth because such events would have a distinct seismic signal — a straight line. This would be caused by the large ratio of speed to the speed of sound in the earth. Herrin estimates that strange quark matter might pass through the earth at 250 miles per second, 40 times the speed of seismic waves. The team also determined that the minimum requirement for detection of a nuclearite would be detection of its signal by seven monitoring stations.

In their new paper, the SMU researchers describe two seismic events with the linear pattern they were looking for. One event occurred on Oct. 22, 1993, when something entered the Earth off Antarctica and left it south of India .73 of a second later. The other occurred on Nov. 24, 1993, when an object entered south of Australia and exited the Earth near Antarctica .15 of a second later. The first event was recorded at seven monitoring stations in India, Australia, Bolivia and Turkey, and the second event was recorded at nine monitoring stations in Australia and Bolivia.

“We can’t prove that this was strange quark matter, but that is the only explanation that has been offered so far,” Herrin said.

The SMU team is now trying to determine where the heavy quark matter may have come from. In April 2002, two different teams of scientists reported that they had identified collapsed stars that might be composed of ultradense strange quark matter. Scientists believe that chunks of strange quark matter might be created when stars made of strange quark matter collide.

Unfortunately, Herrin notes, seismologists may not be able to find any more events that suggest the passage of strange quark matter through the Earth. In 1993 the U.S. Geological Survey stopped collecting data from “unassociated events” such as those that the SMU team used in its research.
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I first posted this article pre-2010, and just checked the links which are non-functional. When I have some more time I will attempt to find the original source material. Richardb