PASADENA, Calif.—The City of Pasadena and Caltech are teaming up to create a citywide fiber optic earthquake detector capable of mapping how temblors are shaking the city at millimeter-scale resolution. The work will take advantage of two currently unused—or "dark"—strands of Pasadena's fiber optic cable that stretch in a large loop around the city. Using a couple strands of fiber to measure seismic activity will gather data equivalent to over 30,000 seismometers. Only 11 traditional seismometers exist within the city...