{"id":386615,"date":"2010-03-03T13:55:21","date_gmt":"2010-03-03T18:55:21","guid":{"rendered":"tag:typepad.com,2003:post-6a00d8341c630a53ef01310f59d3e0970c"},"modified":"2010-03-03T20:32:10","modified_gmt":"2010-03-04T01:32:10","slug":"chilean-quake-shortened-a-day-by-1-26-microseconds-jpl-scientist-says-updated","status":"publish","type":"post","link":"https:\/\/mereja.media\/index\/386615","title":{"rendered":"Chilean quake shortened a day by 1.26 microseconds, JPL scientist says [Updated]"},"content":{"rendered":"

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When an earthquake struck South America last weekend, the ground rumbled in Chile, the sea rose in the Pacific, and a day on Earth got shorter. <\/p>\n

Not by much. <\/p>\n

Earthlings ended up losing 1.26 millionth of a second of a day. You can\u2019t sense it. Nor can your dog — the one you insist senses approaching earthquakes — feel it.<\/p>\n

But while other experts charted the shift of tectonic plates and the swell of ocean waters wrought by the quake, geophysicist Richard Gross mathematically calculated the temblor\u2019s disruption of the day. The thrust quake —\u00a0in which plates underground move vertically — caused mass to move everywhere, according to Gross.<\/p>\n

[Updated at 5:26 p.m.: <\/strong>"On average, the mass of the Earth got a bit closer to the rotation axis," he said.\u00a0 As a result, he said, the planet rotates faster — \u201cjust like a spinning skater brings her arms in closer to her body to rotate faster,\u201d he said. When the planet rotates faster, the day shortens. Gross studies the Earth\u2019s rotation and how it is affected by cataclysmic forces of nature.] <\/p>\n

\u201cAnything that moves mass around on the Earth, I take a look at,\u201d said Gross, who works at the Jet Propulsion Laboratory in La Ca\u00f1ada Flintridge. And it takes a mega-earthquake to attract Gross\u2019 attention. <\/p>\n

The magnitude 6.7 Northridge earthquake didn\u2019t even register on the scale of throwing off the Earth\u2019s rotation. \u201cI didn\u2019t look at that earthquake,\u201d Gross said.<\/p>\n

\u201cIt takes something like the Chilean or Indonesian earthquake before I look at it.\u201d <\/p>\n

While the Chilean quake shortened the day by 1.26 microseconds — the unit of time for\u00a0millionths of a second — the 2004 Indian Ocean earthquake that triggered the catastrophic Asian tsunami shaved 7 microseconds off the day, according to Gross\u2019 calculations.<\/p>\n

Of course, losing just 1.26 microseconds a day would take a couple of millenniums to add up to one single second of lost time. (2,174 years to be more precise.) <\/p>\n

Gross suggests that it\u2019s not worth tallying that way. \u201cIt takes a lot of these big earthquakes to add up to even a second,\u201d he said. \u201cThe bigger changes are in the liquid core within the Earth.\u201d Those changes can throw off a day by a whopping three or four milliseconds, he said. \u201cThose are the things that cause us to have a leap second every year or so.\u201d<\/p>\n

Winds and ocean currents are other forces plying the Earth, changing its shape and the length of its day, according to Gross. <\/p>\n

Far from evoking that textbook illustration of a smooth round ball of continents and blue oceans, Gross describes Earth as a planet of unevenly distributed mass wobbling as it rotates around its imperfectly balanced axis, its physique woefully pear-shaped. \u201cIt\u2019s a bit fatter south of the equator,\u201d he said.<\/p>\n

\u201cThe Earth is not completely elastic. It\u2019s kind of like putty,\u201d he said. \u201cIf you have a sudden shock to it, it will continue to deform later in response to that shock.\u201d <\/p>\n

Gross only mathematically calculated these minute changes in day lengths. He is not sure it can be physically observed, even by sophisticated GPS equipment. \u201cWe have a network of receivers located globally,\u201d he said. \u201cI don\u2019t think those GPS observations are going to be accurate enough. I\u2019m going to look at the measurements, of course, but I would be surprised if I find anything.\u201d<\/p>\n

So why do the math at all? \u201cFor the most part, the Earth\u2019s rotation changes all the time and doesn\u2019t have much practical consequence except here at JPL,\u201d Gross said. \u201cWe need to know this to navigate spacecraft to planets like Mars or Saturn.\u201d Since JPL\u2019s tracking stations for those craft are on Earth, \u201cwe need to know how Earth\u2019s orientation is changing.\u201d <\/p>\n

— Carla Hall<\/p>\n

Map: A representation of the force of the Chilean quake. Credit: NOAA<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

When an earthquake struck South America last weekend, the ground rumbled in Chile, the sea rose in the Pacific, and a day on Earth got shorter. Not by much. Earthlings ended up losing 1.26 millionth of a second of a day. You can\u2019t sense it. Nor can your dog — the one you insist senses […]<\/p>\n","protected":false},"author":4131,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[],"class_list":["post-386615","post","type-post","status-publish","format-standard","hentry","category-news"],"_links":{"self":[{"href":"https:\/\/mereja.media\/index\/wp-json\/wp\/v2\/posts\/386615","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mereja.media\/index\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mereja.media\/index\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mereja.media\/index\/wp-json\/wp\/v2\/users\/4131"}],"replies":[{"embeddable":true,"href":"https:\/\/mereja.media\/index\/wp-json\/wp\/v2\/comments?post=386615"}],"version-history":[{"count":0,"href":"https:\/\/mereja.media\/index\/wp-json\/wp\/v2\/posts\/386615\/revisions"}],"wp:attachment":[{"href":"https:\/\/mereja.media\/index\/wp-json\/wp\/v2\/media?parent=386615"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mereja.media\/index\/wp-json\/wp\/v2\/categories?post=386615"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mereja.media\/index\/wp-json\/wp\/v2\/tags?post=386615"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}