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 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.
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
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.
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.
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.
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.
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.
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.
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
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
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.
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