How can earthquakes shift the earth's axis? One often comes across news articles that claim that an earthquake shifted the earth's axis.

http://news.google.com/?q=earthquake%20shifted%20OR%20shifts%20earth%27s%20axis

If you ignore the influence of other celestial bodies, an internal event like an earthquake surely can't change the direction of the angular momentum of the Earth (unless stuff is ejected out of Earth), since angular momentum has to be conserved in the absence of an external torque. So the axis has to remain fixed.
Am I missing something? Or are geologists trying to say that the resulting movement of tectonic plates causes a change in the point of intersection of the axis (which remains the same) and the plates that include the poles, so that it seems as if the axis has shifted?
EDIT
Some articles mention the value of the shift in the axis and also the change in the length of the day. If, as Ted Bunn's answer indicates below, the shift in the axis isn't actually real but is because of the movement of tectonic plates with respect to the axis, shouldn't the shift be different at the north and south poles? How are the shifts and the change in day-length calculated?
 A: There is some confusion about the term axis.  The axis about which the Earth rotates of course did not change. It requires some external torque or transfer of angular momentum for that to happen.  However, the Earthquake changed the shape of the Earth slightly, which changed the figure axis of the Earth.

Calculations also show the Japan quake should have shifted the position of Earth’s figure axis (the axis about which Earth’s mass is balanced) by about 17 centimeters (6.5 inches), towards 133 degrees east longitude. Earth’s figure axis should not be confused with its north-south axis; they are offset by about 10 meters (about 33 feet). This shift in Earth’s figure axis will cause Earth to wobble a bit differently as it rotates, but it will not cause a shift of Earth’s axis in space-only external forces such as the gravitational attraction of the sun, moon and planets can do that.

Source: http://www.jpl.nasa.gov/news/news.cfm?release=2011-080
A: Your explanation is right: an earthquake can't change the axis of rotation, relative to a given inertial reference frame -- that is, the axis of rotation doesn't change relative to the "fixed stars" as a result of the earthquake. What the earthquake does is to move material around within the Earth, so that the position of the rotation axis relative to any given marker on Earth's surface changes.
If you prefer, rather than saying the earthquake shifted the Earth's axis, you can say that it shifted all of the stuff on the Earth's surface. Since we find it more convenient (often!) to use points of reference that are fixed to markers on Earth's surface, it looks to us like a shift in the axis.
A: Angular momentum doesn't change, but the angular velocity vector does. This is effectively due to a shift in the body's moment of inertia tensor.
A: There is a confusion in the words "axis of rotation". These words have been used for the vector "angular momentum", which doesn't change in absence of external torque or forces. The other vector is the vector "instantaneous rotation", which can change its orientation during the movement, even if the rotating solid doesn't change its shape or mass distribution. Changing the center of gravity during the movement (as a result of earthquaques in our case) can also change that vector, but not the angular momentum. 
