Clip from Haeundae 2009 (Korean for Megatsunami)
https://youtu.be/2QEEyiB3g8k (6:49 minutes)
CSZ – Cascadia Subduction Zone, a result of ongoing research, discussion, reporting and media reports are coming out on a daily basis. It can be very daunting, even depressing to keep up our knowledge about the ongoing scientific research and growth in knowledge about seismicity, and particularly in the CSZ – Cascadia Subduction Zone. Much information and research is coming from Canada, Iceland, Japan and the United States.
So, what is an M9 Megaquake? You will find the answers and much more from Teaching Quantitative Skills in the Geosciences - resources for undergraduate students and faculty by Carleton College, One North College Street, Northfield, Minnesota 55057
So, what is a Megatsunami? From Wikipedia A megatsunami is a term used for a very large wave created by a large, sudden displacement of material into a body of water.
Megatsunamis have quite different features from other, more usual types of tsunamis. Most tsunamis are caused by underwater tectonic activity (movement of the earth's plates) and therefore occur along plate boundaries and as a result of earthquake and rise or fall in the sea floor, causing water to be displaced. Ordinary tsunamis have shallow waves out at sea, and the water piles up to a wave height of up to about 10 metres (33 feet) as the sea floor becomes shallow near land. By contrast, megatsunamis occur when a very large amount of material suddenly falls into water or anywhere near water (for meteor impact), or are caused by volcanic activity. They can have extremely high initial wave heights of hundreds and possibly thousands of metres, far beyond any ordinary tsunami, as the water is "splashed" upwards and outwards by the impact or displacement. As a result, two heights are sometimes quoted for megatsunamis – the height of the wave itself (in water), and the height to which it surges when it reaches land, which depending upon the locale, can be several times larger.
Modern megatsunamis include the one associated with the 1883 eruption of Krakatoa (volcanic eruption), the 1958 Lituya Bay megatsunami (landslide into a bay), and the wave resulting from the Vajont Dam landslide (caused by human activity destabilizing sides of valley). Prehistoric examples include the Storegga Slide (landslide), and the Chicxulub, Chesapeake Bay and Eltanin meteor impacts. The 1958 Lituya Bay megatsunami occurred on July 9 at 22:15:58, following an earthquake with a moment magnitude of 7.8 and a maximum Mercalli Intensity of XI (Extreme). The earthquake took place on the Fairweather Fault and triggered a rockslide of 30 million cubic metres (40 million cubic yards, and about 90 million tons) to fall from several hundred metres into the narrow inlet of Lituya Bay, Alaska. The impact was heard 50 miles (80 km) away, and the sudden displacement of water resulted in a megatsunami that destroyed vegetation up to 525m (1,722 feet) above the height of the bay and a wave that traveled across the bay with a crest reported by witnesses to be on the order of 98 feet (30 m) in height. This is the most significant megatsunami and the largest known in modern times. The event forced a re-evaluation of large wave events, and recognition of impact, rockfall and landslide events as a previously unknown cause of very large waves.
USGS – United States Geological Survey - Contact
The scale was developed in the 1970s to succeed the 1930s-era Richter magnitude scale (ML). Even though the formulae are different, the new scale retains a similar continuum of magnitude values to that defined by the older one. As with the Richter magnitude scale, an increase of one step on this logarithmic scale corresponds to a 101.5 (about 32) times increase in the amount of energy released, and an increase of two steps corresponds to a 103 (1,000) times increase in energy. Thus, an earthquake of MW 7.0 releases about 32 times as much energy as one of 6.0 and 1,000 times that of 5.0.
The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of the area that slipped.
Since January 2002, the MMS has been the scale used by the United States Geological Survey to calculate and report magnitudes for all modern large earthquakes.
Popular press reports of earthquake magnitude usually fail to distinguish between magnitude scales, and are often reported as "Richter magnitudes" when the reported magnitude is a moment magnitude (or a surface-wave or body-wave magnitude). Because the scales are intended to report the same results within their applicable conditions, the confusion is minor.
The United States Government through the US Geological Service maintains a world wide record of seismic events.
Latest Earthquakes - USGS Earthquake Hazards Program [1 Day, Magnitude 2.5+ Worldwide] [http://earthquake.usgs.gov/earthquakes/map/]