The American newspaper “The New York Times” published a report in which it talked about the inner core of the Earth and its characteristics, which were discovered by geologists by studying earthquakes.
The newspaper said, in its report, which was translated by “Arabic 21”, that the geology books clearly include a detailed plan of the earth that shows four precisely defined layers: the outer crust on which all living creatures, including humans, live and consist of solid rocks; the mantle, where magma flows that drive continents and raise mountains; an outer core consisting mainly of iron and nickel, which generates the planet’s magnetic field; Finally, a solid inner core.
When analyzing the intersection of seismic waves from large earthquakes, two Australian scientists confirmed the existence of a completely different layer at the center of the Earth. “We have now confirmed the existence of a deeper inner core,” said scientist Hrvoj Tcalcic, professor of geophysics at the Australian National University in Canberra.
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The newspaper stated that the estimates of Dr. Rvoj Tkalcik and Tan Son Pham indicate that the width of the innermost inner core is about 800 miles, and the width of the entire inner core is about 1500 miles. Their findings have been published in the journal Nature Communications.
The detailed diagram depicts well-defined divisions, but very little data is available on the innermost inner core.
This core is about four thousand miles from the center of the Earth, and it is impossible to drill more than a few miles into the Earth’s crust. Most of what is known about what lies beneath this crust comes from seismic waves — the vibrations of earthquakes that travel across and around the planet.
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According to the paper, two Harvard seismologists, Miyake Ishii and Adam Dionsky, first proposed the idea of a deeper inner core in 2002 based on the peculiarities of the speed of seismic waves passing through the inner core. Scientists have confirmed that the speed of seismic waves that travel through this part of the earth varies according to the direction, as the waves move faster when moving from one pole to another along the earth’s axis, but are slower when traveling perpendicular to the axis. Accordingly, geophysicists believe that the difference in velocities – a few percent faster along the polar tracks – arises from the alignment of the iron crystals in the inner core.
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Harvard seismologists said that the slowest waves are those that move at an angle of 45 degrees to the axis instead of 90 degrees, if they are found in a small region in the center. The data available at the time was so scarce that not everyone could be convinced of its results.
The newspaper added that seismic waves that travel from the origin of the quake directly to the ground and through the innermost inner core will be the best measurements. But figuring that out would require placing a seismometer on the other side of the Earth, in the middle of the ocean.
The newspaper confirmed the possibility of seismic waves rebounding. A seismometer close to the epicenter can detect the reflection of a wave that has passed through the Earth and bounced back, passing the innermost core twice. It can also be reflected back and forth a second time, traveling through the inner core four times.
In recent years, a large number of seismographs have been deployed, especially in the United States. The combination of signals from multiple instruments made it possible to detect faint reflections from earthquakes of magnitude 6 or greater. In this context, Dr. Tkalcik said, “We processed 200 events and found that 16 of them are behind these backscattering waves.”
And in one of the earthquakes that erupted in the Solomon Islands in 2017, waves that traveled five times through the innermost core were detected by seismometers serendipitously placed on the other side of the planet.
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The newspaper quoted Georg Helfrich of the Institute of Earth and Life Sciences at the Tokyo Institute of Technology in Japan, who was not involved in the research: “They deserve this fame after revealing observations that further studies may use to uncover confusion surrounding the concept of the structure of the Earth’s inner core.” There does not appear to be any significant difference in composition between the outer parts and the innermost inner core. Transition also appears to occur gradually rather than abruptly.
For his part, said Vernon Cormier, a professor of physics at the University of Connecticut who was not involved in the research, that this matter may indicate what happened to the Earth in the past, indicating that the inner core is somewhat recent in geological terms, as estimates range from 600 million to one billion. years, which is a small part of the planet’s history of 4.5 billion years. The structure of the solid core also appears to be a bit complicated. And in January, other scientists reported that the spin speed of the inner core was changing.
Dr Cormier added: “The reason behind studying the inner core structure of the Earth is to try to relate it to the planet’s magnetic field. Scientists will try to look for some changes in the Earth’s magnetic field that may have occurred at the same time as the change in crystallization of the inner core.”
https://www.nytimes.com/2023/02/23/science/earth-core-seismic-waves.html