A series of small earthquakes broke Wednesday and early Thursday about eight miles northeast of Julian, causing shaking that was felt across a wide area of the county, the U.S. Geological Survey said.
The shaking began at 4:33 p.m. on Wednesday when a 4.0 quake occurred nearly 10 miles beneath the earth’s surface, just east of the Earthquake Valley fault, one of the most active systems in Southern California. The temblor had originally been listed at 4.2.
The main shock was followed five minutes later by a 3.0 aftershock in the same spot. Then a 3.6 quake occurred near the same spot at 7:57 p.m. Wednesday.
Seismologists say that a 3.6 quake broke in the same area at 2:32 a.m. on Thursday, continuing the seismic spasm.
The first quake drew the greatest amount of attention. it was felt in Julian, Warner Springs, Del Mar, Poway, Alpine, Borrego Springs, Ranchita, San Diego, San Marcos, Jamul, La Mesa, Spring Valley, La Jolla, Ramona, Bonita, Encinitas, Chula Vista, Cardiff by the Sea, Oceanside, National City, Carlsbad, Camp Pendleton, Vista, Lakeside, San Ysidro, Rancho Santa Fe, Escondido, and El Cajon, the USGS said.
“We felt (the) floor shaking on the 7th floor of Jacobs Hall (at UC San Diego),” said Ioana Patringenaru, a campus spokesman. “It was fairly mild and followed by another mild wavy motion.”
Tom Rockwell, a seismologist at San Diego State University, said “This was probably on the Earthquake Valley fault, which is a parallel strand to the Elsinore system. It has about the same slip rate as the Elsinore. It can produce large earthquakes, and might have produced the historical 1890 earthquake, which was 6.3 or close to that.”