Researchers have already studied the effects of two previous megaquakes – the Sumatra-Andaman earthquake in 2004 and last year's earthquake in Chile. After GRACE was launched in 2002, these were the only earthquakes that had had a measurable effect on the satellites' orbits – until the Tōhoku earthquake.
The most recent megaquake shows that the disturbances of satellite orbits can be used to independently estimate the magnitude and location of earthquakes, along with estimates based on surface seismographs and GPS measurements. The researchers calculated how the relative velocity of the two satellites changed as they passed over the affected region. GRACE records variations in the gravity field due to other processes too, but these background signals change over larger timescales than that of the quake, and so could be identified and subtracted. The leftover signal showed that the rate at which the distance between the two GRACE satellites changed – the so-called range rate – was twice as high in the month after the earthquake as in the month prior to the event.
The researchers then built models of the earthquake using data from seismographs and surface GPS instruments, and estimated what the satellites' range rate would be in these models. They found that a model in which the earthquake was of magnitude 9.1 and occurred in Earth's lower crust came closest to the true range rate. By contrast, conventional estimates have put the Tōhoku earthquake's strength at 9.0 and located it in the upper crust. NASA and DLR, the German space agency, which are joint partners in GRACE, are planning a new mission to measure with greater precision how Earth's gravity field changes. This would allow the satellites to monitor earthquakes with magnitudes as low as 7.5, which occur nearly every month somewhere on Earth.
that can gather strength from distress,
and grow brave by reflection.**
Thomas Paine
LARGEST QUAKES -
This morning -
5.0 SAKHALIN, RUSSIA
Yesterday -
12/11/11 -
6.3 SOUTH SANDWICH ISLANDS REGION
6.7 GUERRERO, MEXICO
5.5 SOUTH OF FIJI ISLANDS
6.7 GUERRERO, MEXICO
5.8 RYUKYU ISLANDS, JAPAN
The strong quake in Mexico killed at least three - The US Geological Service initially estimated the quake at magnitude at 6.8, but downgraded it to 6.7 and then 6.5. A quake of that magnitude is capable of causing severe damage, although the depth of this temblor lessened its impact.
MYSTERY SHAKING -
NEW JERSEY - 12/9/11 - Dozens in New Jersey report feeling earthquake, but US Geological Survey detected none. Floors shook, bottles rattled, bells jingled, and scores of New Jersey residents up and down the state cried "earthquake!" Friday morning. Was this the state’s second rattler in four months? Despite more than 60 residents who claimed to have felt shaking, a spokesman for the U.S. Geological Survey said none of the seismometers stationed around the state picked up even a hint of trembling. "It’s not an earthquake. My guess would be it’s more likely thunder or sonic boom."
New Jersey has been rocked this year by half a dozen extreme weather and geological events, including a 5.8 magnitude earthquake centered in Virginia that shook buildings across the Garden State in August. This time, the first-hand reports began streaming in around 10 a.m. from Egg Harbor, Cranbury, East Brunswick, North Brunswick, Trenton, Somerset, Edison, Plainfield, Piscataway, Iselin, South Plainfield and others. People felt their homes sway and heard glass bottles clinking for between 10 and 30 seconds. A band of thunderstorms off the state’s coastline or covert activities at Fort Dix or McGuire Air Force Base in southern Jersey might be possible explanations for what residents might have felt. But a spokesman for the National Weather Service said its unlikely that even severe thunderstorms could make the ground feel as through it’s shaking. Fighter jets used in drills near Virginia and North Carolina have caused sonic booms — the noise and vibration associated with traveling faster than the speed of sound — which can be mistaken for earthquakes. A spokesman for Fort Dix did not return calls for comment.
TSUNAMI / FREAK WAVES / ABNORMAL TIDES -
Japan quake-tsunami recast undersea terrain - Undersea views reveal that Japan's colossal earthquake ripped deep fissures in the seafloor and raised undersea cliffs hundreds of feet, while spawning waves that destroyed billion-dollar seawalls. In a series of reports on the March 11 earthquake, among the strongest ever recorded at magnitude 9.0, researchers at the American Geophysical Union meeting described a shattered world on the Japanese seafloor that birthed a killer tsunami responsible for the deaths of at least 20,000 people. "They were doomed to start with." A $1.6 billion undersea breakwall outside the town of Kamaishi, for example, "didn't protect the town", taking perhaps 6 feet off of a 40-foot tsunami wave. Funneled by narrow sea canyons, waves as high as 130 feet hit some towns, powered by the seafloor's abrupt piston-like bucking during the quake.
"In some places, we cannot see to the bottom of the fissures." Before-and-after robot submarine visits to three sites about 70 miles off Japan's coasts confirm that the seafloor shifted more than 70 feet eastward and dropped more than 30 feet in some locales, along the fault between the Pacific Ocean and the Japanese crustal plate. Fissures stretch the length of football fields and a cliff several hundred feet tall looks freshly exposed at one spot, more than 2 miles deep. "It was a peaceful seafloor, but after the earthquake everything moved." The seafloor study, and satellite images reported Monday, help further explain the tsunami's severity.
• Parts of the seafloor on the eastern side of the fault dropped, while the far side popped upward and westward, delivering a double-barreled tsunami.
• The NASA Jason-1 oceanographic satellite revealed waves merging offshore to heights far exceeding expectations, channeled by undersea ridges. "We call them fingers of God."
• Preventive measures such as planting stands of pine trees on coasts proved useless for stemming waves. Japanese researchers reported that they now realize that a tremendous tsunami that struck Japan in 869 A.D. should have served as a warning to the island nation.
The earthquake struck with such force, the fourth-largest one ever measured in the world by seismologists, that it dealt Japan two waves of shaking: one originating at the fault itself and one emanating from a displaced reflection of the quaking, which shook the seafloor closer to the coast. "It was like an orchestra, with the tubas playing on one side," and the flutes playing on the other. The quake lasted for three minutes, "an enormous amount of time for an earthquake", precisely because of the undersea orchestration of the quake shaking the seafloor. "The more we understand the physics of earthquakes and tsunamis, the better we can warn people the next time. That is why we study this."
TROPICAL STORMS -
No current tropical storms.
SPACE WEATHER -
December 10 lunar eclipse - Lunar eclipses offer a unique way to assess the global dustiness of Earth's stratosphere. The scattering action of dust casts a red light into Earth's shadow. Lots of dust yields a deep red eclipse, while less dust produces a bright coppery hue. The bright copper color of Saturday's eclipse suggests that the stratosphere is relatively clear. "It appears the clear stratospheric conditions of recent years is continuing." This is important because the stratosphere affects climate; a clear stratosphere "lets the sunshine in" to warm the Earth below. At a 2008 conference it was reported that, "the lunar eclipse record indicates a clear stratosphere over the past decade, and that this has contributed about 0.2 degrees to recent warming." ( Eclipse gallery)
