Question

Clear Answer Please: Compared to the other plate boundaries, convergence boundaries often produce the largest earthquakes. Explain why this is so. Is this the only boundary type that produces damaging earthquakes? If so, explain why. If not, describe an example in which another type of boundary has produced a damaging earthquake.

Answer 1

Answer:

The Tectonic plate boundaries are of three types, which are:

1. Convergent (subduction zones and thrust faults) boundaries, where plates move towards eachother;

2. Divergent (spreading ridges) boundaries ( plates move away from each other)

3. Transform (strike-slip faulting) plate boundaries (plates slide past one another)

Most large earthquakes occur at boundaries where the tectonic plates are moving toward each other (Ex in Alaska and Japan), or sliding past each other (ex in Southern California and turkey).

Smaller earthquakes occur where the plates are moving apart, such as mid oceanic ridges.

· Earthquakes at convergent boundaries are caused by compression. This means that any earthquake will only occur when the stresses are high enough to cause the rocks to ride over the top of each other. These earthquakes can reach much higher magnitudes (e.g., Chile in 1960, Indonesia in 2004, Japan in 2011), and tend to affect wider areas. This is partly because of thicker crust and partly because of the stored energy (stress) needed to generate the earthquake.

· Convergent boundaries, by their very nature, are able to store much more energy due to the greater fault plane area that can become locked (on the order of 10s of thousands of square miles).

· In short, it is easier (requires less energy) to pull rocks apart then it is to break them by pushing them together.

· Earthquakes associated with divergent margins are weaker than those at convergent margins because it requires less energy to pull rocks apart than it does to break them by pushing them together.

· Earthquakes at divergent boundaries tend to be low in magnitude. They are mostly generated by volcanic activity, and rarely exceed M5.5.

The Large magnitude earthquakes can also occur along the Transfrom Plate boundaries. (Ex:

· The amount of energy that an earthquake can release is dependent on the total area of the fault plane that breaks. “Normal” dip-slip and “Transform” strike-slip structures can only store so much energy before breaking; the former rarely exceeding magnitude 7 and the latter capable of reaching into the low 8 range.

· By comparison, strike-slip Transform boundaries such as the San Andreas fault are near vertical structures, and though they may be hundreds of miles in length, are limited to in “width” to roughly 10 miles (the average thickness of the crust), and are therefore limited to the amount of energy they can store up.

· Along the Sandreas fault (Strike slip fault boundary), where the pacific plate is sliding north relative to the North American Plate most significant and damaging earthquakes happening everytime. The most powerful California earthquake in recorded history occurred in 1857, about 45 miles northeast of San Luis Obispo near Parkfield, California. Estimates for the quake's magnitude range from 7.9 to 8.3.

In Summary:

At convergent plate boundaries, where two continental plates collide earthquakes are deep and also very powerful. In general, the deepest and the most powerful earthquakes occur at plate collision (or subduction) zones at convergent plate boundaries.

Transform plate boundaries, have shallow, but very powerful earthquakes.

At divergent plate boundaries, earthquakes tend to be weak and shallow.

For visual understanding of relation of Earthquakes with different plate boundaries, few images have been attached below;