One unexpected side effect of our giant urban oil field: sometimes oil and gas companies (like Signal Hill Petroleum in this case) create incredibly thorough monitoring systems that end up picking up a bunch of interesting earthquake information. In 2011, "a whole host of little earthquakes in L.A. rippled through the basin," and Signal Hill's network of instruments (seismometers were placed just 100 meters apart from each other) "captured them in unprecedented detail," according to Trembling Earth (via io9). Scientists at Caltech and Berkeley made a deal with the company to get a look at the data and created this awesome video showing "the elastic (seismic) waves of several earthquakes as they propagate from the hypocenter and rock the city block by block." (The four earthquakes start at 0:45, 2:20, 6:00, and 8:35). The line you see running diagonally on the map is the Newport-Inglewood Fault, the strike-slip fault that was responsible for the 1933 Long Beach earthquake. When the waves cross the fault, "they get held back and slowed down, forming an irregular jog or knick in the wavefield." More on all the science behind this over at TE.
· Watch the ground ripple in Long Beach [Trembling Earth]