It is widely accepted that Earth's inner core is solid but the idea had never been conclusively proved. Nu, forskere…
It is widely accepted that Earth’s inner core is solid but the idea had never been conclusively proved. Nu, forskere har fundet shear waves i den indre kernen og brugte dem til at undersøge vores planet’s interiør.
Shear waves or “J waves” is a type of wave that can only travel through solid objects.
“We found the inner core is indeed solid, but we also found that it’s softer than previously thought,” said Professor Hrvoje Tkalčić from Australian National University (ANU). It turns out – if our results are correct – the inner core shares some similar elastic properties with gold and platinum. The inner core is like a time capsule, if we understand it, we will understand how the planet was formed, and how it evolves. “
The inner core is Earth’s deepest layer, which is surrounded by a liquid outer core. Det er blandt de endelige grænser for at forstå historien om jorden. Men den største utfordringen er højtryk og ekstreme temperaturer.
Shear waves can also provide information on inner core’s solidity and its composition. Men de bølger i indre kerne er så små og svake, de kan ikke bli observert direkte. Onderzoekers ontwikkelden een creatieve aanpak om J waves in de aardbeving coda correlatie wavefield te detecteren. The method originally looks at the similarities between the signals at two receivers after a major earthquake.
“We are throwing away the first three hours of the seismogram and what we are looking at is between three and 1
0 hours after a large earthquake happens. We want to get rid of the big signals, “said Dr. Tkalčic.
” Using a global network of stations, we take each single receiver pair and every single large earthquake – that’s many combinations – and we measure the similarity between the seismograms . That’s called cross correlation, or the measure of similarity. Af disse ligheder kan vi opbygge et globalt korrelogram – en slags fingerprint af jorden. “
Disse resultater kan bruges til at bestemme eksistensen og hastigheden af J-waves i den indre kerne, som i sidste ende kunne hjælpe med at svare på nogle grundlæggende spørgsmål om dette region.
“For example, we do not know yet what the exact temperature of the inner core is, what the age of the inner core is, or how quickly it solidifies, but with these new advances in global seismology, we are slowly getting there, “said Dr Tkalčić.
” The understanding of the Earth’s inner core has direct consequences for the generation and maintenance of the geomagnetic field, and without that geomagnetic field there would be no life on the Earth’s surface. “