GEL 1 Lecture Notes - Lecture 19: Earthquake Early Warning (Japan), Thrust Fault, Subduction
monitoring background wave w/ buoy
tsunami wave height anomoly
Tohoku quake March 1, 2011
M9.0 earthquake along Japanese trench (oceanic-oceanic convergent plate margin)
●subduction zone 'megathrust' - thrust fault / convergent boundary producing
faulting where you have compressional forces
●fault moving after being locked for a long time has a jerky motion - many large
aftershocks
●focus - 30 km below the surface
●Earthquake Early Warning System - 31 second notice to measure earthquake and
send message to people - not enough time
●epicenter in ocean - rapidly displaces sea water
○rupture zone is along the fault plane (500 x 200 km)
○seabed moved 24m horizontally and 3m upward
■precise gps measurements
●tsunami wave propagates across entire ocean basins
○nuclear meltdown disaster at Fukushima
○inundation 10km inland
○up to 40 m tsunami wave
○went all the way across Drake's passage - stormy sea waters at SA's tip
○18,000 people died
TSUNAMI DETAILS
●a sea wave with very long (100+km) wave length
○not necessarily wave height
○caused by rapid displacement of seawater
■earthquakes or landslides
●NOT seismic waves moving through water
●NOT tidal waves
●Propagation
○easily travel through open ocean
○runup near the shore (along continental shelf) causes wave length
compression and thus vertical displacement (large effective wave heights)
■shallow coastal shelf/broad continental shelf → greater tsunami wave
heights
■wave slows down but still has same energy, goes up
Tohoku tsunami reached west coast of America in 9-10 hours, with surges of 2.4 meters
$70 million in damage and 1 death in Cali
●megathrust earthquakes
Document Summary
Monitoring background wave w/ buoy tsunami wave height anomoly. M9. 0 earthquake along japanese trench (oceanic-oceanic convergent plate margin) Subduction zone "megathrust" - thrust fault / convergent boundary producing faulting where you have compressional forces. Fault moving after being locked for a long time has a jerky motion - many large aftershocks. Focus - 30 km below the surface. Earthquake early warning system - 31 second notice to measure earthquake and send message to people - not enough time. Epicenter in ocean - rapidly displaces sea water. Rupture zone is along the fault plane (500 x 200 km) Seabed moved 24m horizontally and 3m upward. Tsunami wave propagates across entire ocean basins. Went all the way across drake"s passage - stormy sea waters at sa"s tip. A sea wave with very long (100+km) wave length. Runup near the shore (along continental shelf) causes wave length compression and thus vertical displacement (large effective wave heights)
