Large-scale earthquakes where the Juan de Fuca plate is being subducted beneath

Question

Large-scale earthquakes where the Juan de Fuca plate is being subducted beneath the west bound slab of the North American plate generates tsunamis of unbelievable size. Because there is no historic written record in North America of these tsunamis, geologists have developed several other means by which to locate and evaluate these ancient events. What are several ways that tsunamis leave us a record and which do you think affords us the greatest detail of the quake and the subsequent seismic sea wave?

This link will help you if you need more ideas:
http://www.burkemuseum.org/static/earthquakes/bigone/detective.html

Explanation / Answer

Most of the time earthquake near the coastal area brings the tsunami with them. We know that the water brings by tsunami that rush the area is of very high energy therefore it is expected that this water will brings the large grains of sand and pabble with it. As the Tsunami rushed into deeper costal areas it will deposited this sand and large pabbles with it and this sand layer will act as one of the marker that indicate that area under investigation has face the Tsunami in the past.

During the Tusnami most of the land biota sink in the water and make the soil rich in organic matter. Therefore these organic rich mud become darker with time and later with time may convert to coals. hence very thin layer of these darker muddy layer or organic layer underneath the surface is also indicative of the paleo tsunami.

The dead trees drawned during Tsunami are also indicative of the paleo quakes and tsunami genertion due to them.

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