Earthquakes are much more common on the west coast of the United States. To understand why this is, we first need to understand what causes an earthquake.

Earthquakes occur along faults, which are where two pieces of rock slide past each other. Most of the time the rocks on each side of a fault are not moving, but when the rocks do move, the result is an earthquake.

An earthquake is the release of energy that builds up while the rocks along a fault aren’t moving. For example, think about pressing your hands together really hard and then moving them in opposite directions while still pressing. At first when you try to move your hands, it might be difficult and you might have to try a little harder to move them past each other, but eventually your hands will slide and make a slight sound. In this example, your hands are like the rocks on either side of a fault. You are using energy to try to move your hands past each other and when they eventually move, the sound that's made is a release of energy, kind of like an earthquake.

Now, the biggest faults in the world are typically found between tectonic plates, which are essentially giant, continent-sized pieces of rock that make up the surface of the earth. One fault that exists between tectonic plates that you may have heard of is the San Andreas Fault in California (which is about 50 miles from where I live!). Over long periods of time, tectonic plates collide into each other and cause even more faults to form inside the tectonic plates! On the west coast, there are multiple continental plates that are colliding and moving past each other right now (the North American plate, Pacific plate, and Juan de Fuca plate), so there are a lot of faults.

The east coast, on the other hand, consists of just the North American plate, so there are a lot fewer faults. Therefore, since the west coast has more faults than the east coast and has multiple tectonic plates that are colliding into each other, there are many more earthquakes on the west coast.

There are more earthquakes on the West coast of the United States, because the boundaries of the North American, Pacific, and Juan de Fuca tectonic plates are located there.

As the edges of the plates slide past or are forced under each other, the movement creates earthquakes. The East coast is not near any tectonic plate boundaries, so there is less to cause rocks to move and as a result, fewer earthquakes. That said, the relative lack of faults on the East coast means that when earthquakes do occur, the energy from them can travel through the ground a very long way, and people further away from the source of the earthquake can feel it. On the West coast, there are many faults, which allow energy from earthquakes to disperse more easily, so you have to be closer to an earthquake to feel it.

Earthquakes happen more often along the west coast of the United States because the west coast is situated on the boundary of some major tectonic plates. Tectonic plates are HUGE moving rock masses that make up the Earth's crust. Earthquakes are caused by these plates moving and grinding against each other. The east coast of the United States is farther away from where these plates meet one another, so earthquakes are less common there.

Earthquakes are most common where two tectonic plates rub against each other along a fault line. While the surface of the earth seems stationary, the plates actually are continuously moving (just very slowly). As they move, they can get snagged on one another, building tension. Once this “snag” breaks free, the tension is released, causing an earthquake.

The west coast of the United States is either sliding along or sliding on top of the Pacific Plate, one of the tectonic plates in the Earth's crust (just as continents move, so do ocean floors). These movements as the two plates slide across one-another create earthquakes. As a result the west coast produces a lot of earthquakes.

The east coast of the United States is joined to the same plate as what makes up the western Atlantic Ocean. Because they are a single plate, not two plates sliding past, there are many fewer earthquakes. Most of the earthquakes that do happen in the east happen because the east coast used to be two plates, before about 250 million years ago, and the collision between those two plates created the Appalachian Mountains. You can think of the Appalachians still remembering being part of two plates, and sometimes making earthquakes for old times' sake.

Based on the data we have on Earthquakes ( here ) in the United States that are magnitude 7 or above (Magnitude 7+ and 8+ on that site under "All Earthquakes -> United States) and the table of Earthquake Counts by State 2010-2015), earthquakes are much, much more common on the West Coast. As to the reason, one possible explanation is that pieces of the Earth's outer crust move, and there are three such pieces intersecting each other on the West Coast of the United States but not on the East Coast ( read more here ).

We can imagine that when such large pieces of ground move against each other, the ground on which we stand will be disturbed greatly, generating earthquakes.

We have big mountain ranges on the West coast, where continental plates are pushing up against each other. The movement of these plates causes earthquakes. The East coast has only small mountain ranges and some small earthquakes.

This is an interesting article which I recommend for you to read.