‘Wobble’ may precede some great earthquakes

Science Daily  April 29, 2020
The land masses of Japan shifted from east to west to east again in the months before the strongest earthquake in the country’s recorded history, a 2011 magnitude-9 earthquake. An international team of researchers (Germany, Chile, USA- Ohio State University) analyzed the “wobble,” may have the potential to alert seismologists to greater risk of future large subduction-zone earthquakes. The imperceptible movement was obvious in data recorded by more than 1,000 GPS stations distributed throughout Japan, in the months leading up to the March 11 Tohoku-oki earthquake. They saw a reversing shift in the land — about 4 to 8 millimeters east, then to the west, then back to the east. Those movements were markedly different from the steady and cyclical shifts the Earth’s land masses continuously make. The wobble could indicate that in the months before the earthquake, the plate under the Philippine Sea began a “slow slip event,” a relatively gentle and “silent” underthrusting of two adjacent oceanic plates beneath Japan, that eventually triggered a massive westward and downward lurch that drove the Pacific plate and slab under Japan, generating powerful seismic waves that shook the whole country. But it will not be possible to use the findings of this study to predict earthquakes in some subduction zones around the world because they do not have the GPS systems needed…read more. TECHNICAL ARTICLE