ANNUAL SEISMICITY

Year-long Views of Seismic Activity in Southern California

Below are links to animations and still images of all recorded seismicity, divided into standard calendar years, for the area of southern California between 32° and 36° N latitude and 114.75° to 121° W longitude. Each still image spans a full year; each animation covers an entire year as well, with each frame representing one week (the days are measured in Pacific Standard Time). The frames in these animations are labelled using two month/day pairs to define each week period, and to give viewers a meaningful reference frame. Bear in mind that these divisions mean little to the forces driving these events.

The earthquakes in the animations appear as colored dots, outlined in black, on a light grey and blue background map of southern California, with major highways shown in tan and towns labelled in white. The size of the dots scales proportionally with the magnitude of the quakes. A color scale denoting magnitude is also provided. For the animations, you may choose no background for minimal interference (and also minimal reference), but all still images are shown with the background.

Below each link is a short description of that year's characteristics, which generally includes the magnitude and location of the largest events and the on-going sequences of activity visible in that animation or image. Within the animations themselves, particularly large or significant earthquakes with be labelled, and will appear as rings if they would normally be hidden beneath the symbols of their aftershocks. Within the still images, these quakes will either be "buried", or shown using "transparent" symbols. The animations will linger slightly on frames with labelled quakes.

Note: Should you have problems getting an animation to work the first time, try reloading the page. (Reloading will also restart the animation.) To replay the animation, use your browser's "Back" button, and then go "Forward". Unfortunately, some browsers may not align the animations correctly.

1985 Still Image

In terms of large earthquakes, 1985 was a very quiet year. The two largest quakes to strike southern California this year were a magnitude 4.8 just south of Fontana on October 2nd, and a magnitude 4.6 near Bakersfield on February 7th. Both of these earthquakes are at least partially visible in this image.

1986 Still Image

Two earthquakes greater than magnitude 5 struck southern California in 1986, both in the month of July. The first and larger was the North Palm Springs earthquake on the 8th of that month. This magnitude 5.6 event on the eastern section of the Banning fault zone (or possibly on the Garnet Hill fault) caused considerable damage in the epicentral area. It produced a sizable aftershock sequence, and indeed, the symbol of the mainshock in this image is entirely buried beneath its aftershocks' symbols. The second damaging earthquake in July 1986 was the Oceanside earthquake, a magntiude 5.4 event on July 13th. This earthquake also had a large aftershock sequence, which can be seen as a cluster of epicenters offshore from Oceanside. The Oceanside event may have led to the October 28th, magnitude 4.6 event just south of San Diego, which can be easily seen near the bottom of this image.

1987 with no background still image only

Three sizable earthquakes struck southern California in 1987. The first, Whittier Narrows (M 5.9), came on the first day of October. Its mainshock symbol, though not completely buried by aftershocks -- its aftershock sequence was somewhat small for its size -- is visible near Los Angeles as a "transparent" yellow circle. The other two struck in late November, and were part of the same activity. The Elmore Ranch earthquake (M 6.2) hit just twelve hours before the larger Superstition Hills earthquake (M 6.6). Only a tiny portion of each of those symbols would be visible normally, so they too have been represented with transparent symbols, visible just to the south of the Salton Sea. All three of these earthquakes are noted in the animation. Easily visible (offshore) in this animation is the aftershock sequence of the 1986 Oceanside earthquake, decaying very slowly, northwest of San Diego. Also visible is the more rapidly decaying aftershock sequence of the 1986 North Palm Springs earthquake, northwest of Indio.

1988 Still Image

Several earthquakes greater than magnitude 4.5 can be seen in this image of the seismicity of 1988. The largest is the Tejon Ranch earthquake of June 10th, a magnitude 5.4, south of Bakersfield. The next largest is the magnitude 5.0 Pasadena earthquake of December 3rd, in the vicinity of Los Angeles. To the east of that is the 1988 Upland earthquake, a magnitude 4.7 which struck late in June. Its symbol is nearly buried beneath those of its aftershocks. Offshore to the south from Los Angeles, the symbol marking a magnitude 4.8 earthquake on November 19th can be seen along the Palos Verdes fault zone.

1989 Still Image

The largest earthquake in this area in 1989 was the Malibu earthquake, which occurred offshore on January 18th, and had a magnitude of 5.0. Its symbol is barely visible in the Santa Monica bay. The second largest event this year was the Newport Beach earthquake, magnitude 4.7, on April 7th. Its epicenter is right on the coastline, south of Los Angeles. Very near downtown Los Angeles, the symbol for the Montebello earthquake, a magnitude 4.6 on June 12th, and its magnitude 4.4 aftershock (on the same day) can just barely be seen beneath the background seismicity of the Los Angeles basin.

1990 Still Image

The largest event in all of 1990 was the February 28th Upland earthquake, a magnitude 5.4 located east of Los Angeles. Its symbol is hidden by those of its aftershocks, three of which were larger than magnitude 4.5. Aside from this activity, no other earthquakes greater than magnitude 4.5 were recorded in southern California during the rest of 1990.

1991 Still Image April 1991 animation

The largest earthquake in southern California in 1991 was the Sierra Madre earthquake of June 28th, which had a moment magnitude of 5.8 and was located northeast of Los Angeles, deep beneath the San Gabriel Mountains along the Clamshell-Sawpit Canyon fault. It had a fairly small aftershock sequence, so part of its bright yellow symbol can be seen clearly in this image. No other earthquakes greater than magnitude 4.5 -- including aftershocks of the Sierra Madre earthquake -- occurred in this area that year.

1992 with no background still image only

The biggest event of 1992 was, of course, the Landers earthquake (M 7.3) on June 28 -- the largest earthquake to hit southern California since the Kern County earthquake (M 7.5) in 1952. Associated with this major event were three other sizable earthquakes, plus tens of thousands of aftershocks, over a dozen of them greater than magnitude 5. The second-largest earthquake in 1992 was, effectively, the largest Landers aftershock, though it occurred on a separate fault system. That was the Big Bear earthquake (M 6.4), which followed the Landers mainshock by a little more than three hours. The third-largest quake in 1992 was the one which ultimately led to the Landers quake -- the Joshua Tree earthquake (M 6.1) on April 22. The symbols for all three of these quakes are buried in those of the aftershocks which followed (compare this year to any earlier year), and thus are shown with "transparent" symbols, but the fourth largest stands out quite dramatically (in bright yellow) along the trace of the Garlock fault zone. This was the Mojave earthquake (M 5.7) of July 11, which was triggered by the Landers event, despite the delay in its occurrence. This earthquake had surprisingly few aftershocks and is positioned on an obvious "gap" in the low-level background seismicity of the Garlock fault, so it stands out prominently.

1993 Still Image

The magnitude 5.2 Wheeler Ridge earthquake of May 27th was the largest event in southern California in all of 1993. Part of its epicenter symbol is visible south of Bakersfield. The next largest earthquake was a magnitude 5.0 Landers aftershock on August 20th, near the original Landers epicenter (its symbol is visible northwest of Indio). Another notable source of activity was the Parkfield area, at the top of this image, near the northwest corner. The largest earthquake there was of magnitude 4.6, on the 14th of November.

1994 with no background still image only

Of primary interest in this animation of 1994 is, of course, the magnitude 6.7 Northridge earthquake of January 17th. The aftershock sequence of this earthquake dominates the seismicity of the Los Angeles area. The symbol of the mainshock's epicenter is nearly buried beneath the symbols of its aftershocks in this animation, and is completely obscured in the still image (but is shown with a "transparent" symbol). Well to the east of Los Angeles, Landers aftershocks persist with remarkable strength. The largest of the year was a magnitude 5.0 on June 16th; it can easily be seen in this animation. Also, watch for a magnitude 4.9 earthquake near Parkfield (near the northwest corner of map) on December 20th -- the largest event to strike that area this year.

1995 with no background still image only

The Landers and Northridge aftershock sequences continue throughout 1995, weakening gradually. Of new interest in this animation is the start of the Ridgecrest sequence, which begins with a magnitude 5.4 event on August 17th, and peaks with a magnitude 5.8 event on September 20th. Ridgecrest aftershocks persist throughout the rest of the year.

1996 Still Image Graph of Events Per Day

See Monthly Seismicity for 1996 animations.

1997 Still Image Graph of Events Per Day

See Monthly Seismicity for 1997 animations.

1998 Still Image Graph of Events Per Day

See Monthly Seismicity for 1998 animations.

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