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Southern California Earthquake Data Center

Earthquake Information

1997 Monthly Seismicity

January 1997 MAP GRAPH
    January 1997 represents a fairly dull month for southern California. Approximately 880 earthquakes were recorded over these 31 days in the area covered by this animation, but only one was greater than magnitude 3.5 -- a magnitude 3.6 on the 13th, north of the Palomar area (a magnitude 3.8 Coso aftershock -- one of nearly 500 during this month, just north of the map area (i.e. not shown) -- occurred on January 4).

February 1997 MAP GRAPH
    February 1997 was a month of fairly low seismicity, also lacking in significant events. Roughly 690 earthquakes -- a small number, even for the shortest month of the year -- can be seen in this animation (about 300 more occurred just off the map, in the Coso area). The two largest were both magnitude 3.8. One occurred on February 6 near the San Jacinto fault zone, and one on February 22, east of Indio.

March 1997 MAP GRAPH
    In this animation of March 1997, watch for the Calico Earthquake (M 5.1) and its aftershock sequence starting on March 18 near Barstow. This Landers aftershock was the seismic highlight of the month, and its own aftershocks contributed to the higher seismicity rate (compared to the previous month) seen in March -- about 930 earthquakes are plotted in this animation.

April 1997 MAP GRAPH
    Two Northridge aftershocks (M 5.1 and M 4.9) provided much of the excitement for the month of April. In the early morning hours of April 26 and 27, these two quakes woke sleepers across the Los Angeles area and caused some minor damage near their epicenters. In addition, they produced numerous aftershocks and helped raise the seismicity rate in this area to more than 1060 earthquakes over the course of these 30 days.

May 1997 MAP GRAPH
    Aftershocks from the late April Northridge aftershocks continue into May. Also, watch for a magnitude 4.5 south of Lake Isabella on May 6 and a magnitude 4.0 near Ridgecrest on May 23 -- these were the largest events of the month. In all, nearly 950 earthquakes are plotted in this animation.

June 1997 MAP GRAPH
    The number of earthquakes shown in this animation of June 1997 is only about 870, but the month was more notable than many. Starting on the 19th, a series of quakes (the largest, M 4.7) struck near the southeastern tip of San Clemente Island. On the 28th, a M 4.2 earthquake struck the San Bernardino area causing some alarm and numerous aftershocks, but no real damage. At the beginning of the month, you may note some minor, but unusual, activity -- a small cluster adjacent to the San Andreas fault zone in the Carrizo Plain and one rare earthquake located east of Baker.

July 1997 MAP GRAPH
    While perhaps not quite as interesting as the previous month, July 1997 was not short on seismicity. A magnitude 4.3 Ridgecrest aftershock on the 3rd, and a July 25 magnitude 4.8 earthquake along the deeper reaches of the Clark fault (a branch of the San Jacinto fault zone), were the two largest events this month. Activity continued in the San Bernardino area, and a swarm of earthquakes in Mexico, between the southern end of the Imperial fault zone and the northern end of the Cerro Prieto fault, began on the last day of the month. Both contributed to a rise in the seismicity rate, giving July a total of over 1220 earthquakes.

August 1997 MAP GRAPH
    Though August 1997 was a month lacking in large quakes, two swarms in Baja California provided some excitement and a fair amount of activity. One was a continuation of the activity seen at the end of July. The other, which produced fewer earthquakes, occurred along the Sierra Juarez fault zone. These swarms helped bring the seismicity rate to just under 1150 earthquakes this month. The largest earthquake to strike the area, however, did not take place in Mexico, but at the southeastern tip of San Clemente Island. It was a magnitude 3.6 tremor on the 12th.

September 1997 MAP GRAPH
    The seismicity rate in September 1997 dropped noticably from the previous month's count. There were fewer than 840 earthquakes recorded in this area during the course of the month. However, two of these were greater than magnitude 4. The first, a magnitude 4.1 jolt, occurred in the aftershock zone of the 1992 Big Bear earthquake on September 19. The second and larger event, magnitude 4.4, was a Landers aftershock on September 28.

October 1997 MAP GRAPH
    With 830 earthquakes recorded in this area in October 1997, the seismicity rate was low but relatively unchanged compared to the previous month. However, there was only one event larger than magnitude 3.5 recorded. This event, on the 14th, was a magnitude 3.9, strike-slip earthquake along the Fontana trend -- a linear feature identified by frequent small earthquake activity but not associated with a mapped surface trace. (It is probably a left-lateral fault buried beneath the sediments of the San Bernardino Valley.) The quake was widely felt in the region known as the "Inland Empire".

November 1997 MAP GRAPH
    November 1997 featured the lowest rate of seismicity for this area seen in years -- fewer than 610 earthquakes can be seen in this animation. Aside from this simply being a quiet (low background seismicity) month, part of the reason for the low rate comes from the ongoing decay of the Landers and Northridge aftershock sequences, which offer up fewer and fewer events as time passes. The main highlights of this month, unfortunately, were on the edge of our network, and located well north of this animation. These included some exceptional activity in the Long Valley Caldera, and a M 4.7 earthquake east of Big Pine on the 14th. The largest event visible in this animation is a magnitude 3.9 Landers aftershock on November 5, just north of Barstow.

December 1997 MAP GRAPH
    Compared to the previous month, the seismicity rate in southern California rose slightly in December 1997, but, in all, it remained rather low. Roughly 760 earthquakes are shown in this animation. The "honor" of being the largest quake was shared by two events measuring M 4.1 -- one on the 5th of the month near Yucaipa (technically an aftershock of the Landers - Big Bear sequence), and the other in the Brawley Seismic Zone (near Obsidian Butte) on the 31st. This latter event was the high point of about a week of activity along this seismic zone, which runs from the southern end of the San Andreas fault zone, near Bombay Beach, to the northern end of the Imperial fault zone.
End of Year 1997 Summary MAP GRAPH


Division of Geological and Planetary Sciences | California Institute of Technology