SCSNSCSN http://www.scsn.org Southern California Seismic Network Thu, 20 Sep 2018 20:54:57 +0000 en-US hourly 1 https://wordpress.org/?v=4.9.2 08/28/2018, M4.4 near La Verne ../../index.php/2018/08/29/08-28-2018-m4-4-near-la-verne/ ../../index.php/2018/08/29/08-28-2018-m4-4-near-la-verne/#respond Wed, 29 Aug 2018 02:43:55 +0000 http://www.scsn.org/?p=2886 ]]>
  • 28 Aug 2018 19:33:28 PDT, (34.137, -117.775), depth 5.5km, 4km N of La Verne, California
  • Aftershocks: so far (29 Aug 2018, 08:05AM PDT) there have been 37 aftershocks recorded, the largest M3.4 (smallest M0.5). More may be expected in the next few days, the largest expected is approximately 1 magnitude unit smaller than the mainshock. There is a small chance (about 5%) that a larger quake could occur, with the likelihood decreasing over time.
  • Historical seismicity: since our records began in 1932 we’ve had 9 events of M4 or greater within 10km of today’s event, the largest was M5.5 (1990/02/28) and the most recent was M4.5 on 17 Apr 1990.
  • Nearby faults: Sierra Madre fault zone, Sierra Madre E section (Sierra Madre fault) (0.6 km), San Antonio fault (2.5 km), Sierra Madre fault zone, Sierra Madre D section (Sierra Madre fault) (6.5 km), San Jose fault (6.8 km), Sierra Madre fault zone, Sierra Madre D section (Upper Duarte fault) (8.0 km), Stoddard Canyon fault (8.9 km), San Gabriel fault zone, San Gabriel River section (San Gabriel fault) (10.1 km), Sierra Madre fault zone, Cucamonga section (Cucamonga fault) (10.5 km), San Gabriel fault zone, San Gabriel River section (Weber fault) (11.2 km) and Sierra Madre fault zone, Clamshell-Sawpit section (Clamshell-Sawpit Canyon flt) (12.6 km).
  • Links for: USGS earthquake page, ShakeMap, DYFI, waveforms.
  • Visit our special reports page for further information on local notable earthquakes.
  • Below are the waveform data associated with this event, as recorded in our Live Seismograms Feed.

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    The Cahuilla Earthquake Swarm: 2016-2018 ../../index.php/2018/08/24/the-cahuilla-earthquake-swarm-2016-2018/ ../../index.php/2018/08/24/the-cahuilla-earthquake-swarm-2016-2018/#respond Fri, 24 Aug 2018 17:51:44 +0000 http://www.scsn.org/?p=2869 ]]> Update: 24 August 2018
    Egill Hauksson, Zach Ross and Jen Andrews, Caltech; Elizabeth Cochran, USGS Pasadena

    The most recent Cahuilla swarm, which started in mid-2016, has grown steadily in number of events (currently ~6,300 of magnitude larger than 0.3) and presently extends over an almost north-south linear trend of about 7 km. Since late on 11 August 2018 the seismicity accelerated with a 120-event foreshock sequence, which culminated with a mainshock of Mw4.4 on 15 August 2018. The mainshock was followed by more than 200 aftershocks of magnitude larger than 0.3 over a period of 12 hours. This new activity extends the spatial distribution of the sequence about 0.5 km to the southwest. The b-value decreased from ~0.94 to ~0.74 during this most recent activity, suggesting that a new region, possibly of higher state of stress, was being activated.

    This is a fascinating sequence from a scientific point of view but it has almost no immediate hazards implications. It could end up with a M5 event, but a much bigger event is very unlikely.

    The observations that we have so far are:

    1. The sequence started back in June 2016 with small events of magnitude 0.5 to 1.5.
    2. Since June 2016, we have recorded about 6,300 events of magnitude larger than 0.3, and the largest M4.4 occurred 15th August 2018. This is a great area to record small events because there is little traffic noise and the rocks are very solid.
    3. Detailed spatial and temporal evolution of the 2016 to 2018 swarm, using high precision waveform relocated epicenters. Data from the Caltech/USGS Southern California Seismic Network. Note that the scale bar is only 2 km long.

    4. These events are shallow, or 4.5 to 5.5 km deep; but large events on major faults usually start twice or three times as deep.
    5. This activity is not on a major fault but half way between the Elsinore and San Jacinto faults. No major events have occurred here in the past, if it had there would be a fault scarp.
    6. We are not sure what is causing these events. We have looked for fluid injection or extraction but we did not find any evidence. The rocks in the area are solid and it is almost impossible to inject water into them. The likely cause is low tectonic strain from the loading of the San Jacinto or Elsinore faults, which is being absorbed by ancient (maybe as old as 50 million years) geological cracks in the rock.
    7. Two similar earthquakes swarms like this one that occurred in the area in 1980-1981 and 1983-1984 were not followed by bigger events on other faults. The map below shows the time/space evolution of all three swarms. Note the small north-south spatial extent of ~5km for the 2016-2018 swarm. In comparison, the 1992 M7.3 Landers quake extended about 100 km north-south.
    8. Map showing geographic location and time evolution of all three Cahuilla swarms.

    9. Will the activity continue? Yes, but the region is now in an aftershock mode following the M4.4, which means decreasing activity over time. However, there seems to be small (approx. 0.5 km) spatial migration to the southwest, which could cause renewed activity. This would be a new chapter in a still to be completed saga. The plot below shows activity since 1 Jan 2018 to present as magnitude versus date. The red stair-stepping line is the cumulative count of events larger than M1.5, which shows that the rate of events is pretty steady indicating that this sequence is continuing.
    10. Time evolution of the Cahuilla swarm versus magnitude during 2018. The red stair-stepping curve is the cumulative count of events of magnitude larger than 1.49 (see Y-axis to the right). Black circles are scaled with magnitude. Events of magnitude greater than 3.0 are shown as stars, with size proportional to magnitude.

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    08/14/2018, M4.4 near Aguanga ../../index.php/2018/08/15/08-14-2018-m4-4-near-aguanga/ ../../index.php/2018/08/15/08-14-2018-m4-4-near-aguanga/#respond Wed, 15 Aug 2018 01:42:19 +0000 http://www.scsn.org/?p=2847 ]]>
  • 14 Aug 2018 18:24:26 PDT, (33.477, -116.803), depth 1.9km, 7km NE of Aguanga, California
  • Aftershocks: so far (16 Aug 2018, 10:48AM PDT) there have been 435 aftershocks recorded, the largest M2.9 (smallest M0.0). More may be expected in the next few days, the largest expected is approximately 1 magnitude unit smaller than the mainshock. There is a small chance (about 5%) that a larger quake could occur, with the likelihood decreasing over time.
  • There were 95 events during the 3 days prior to the earthquake (within a 10 km radius), the largest was M2.3 (2018/08/12). This area has been experiencing swarm activity for over 2 years (referred to as Cahuilla swarm), seeing elevated seismicity rates since early 2016. This region has hosted earthquake swarms since the 1980s, each lasting for weeks or a few months. The swarm starting early 2016 is the most prolific swarm recorded, with several thousand events observed so far.
  • 2018 seismicity in the region of the Cahuilla swarm as of 15 August 2018. Circles plot individual earthquakes at all magnitudes in the SCSN catalogue, with size indicating magnitude. Events with magnitude 3.0 or greater are shown as red stars. The red line plots the cumulative number of events with magnitude 1.49 or greater.

    Seismicity in the Cahuilla swarm from 1 day before the M4.4 event to approximately 40 hours after. Top plot shows the cumulative event number and the number of events per 20 minutes, both showing the aftershock event rate decay. Bottom plot shows event magnitudes against time.

  • Historical seismicity: since our records began in 1932 we’ve had 13 events of M4 or greater within 10km of today’s event, the largest was M5.6 (2005/06/12) and the most recent was M4.1 on 17 Nov 2008.
  • Links for: USGS earthquake page, ShakeMap, DYFI, waveforms.
  • Visit our special reports page for further information on local notable earthquakes.
  • Below are the waveform data associated with this event, as recorded in our Live Seismograms Feed.The closest station to the earthquake shown in the view is CI.HMT2 near Anza-Borrego at approximately 30km from the epicenter.

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    07/25/2018, M4.2 near Ensenada ../../index.php/2018/07/25/07-25-2018-m4-6-near-ensenada/ ../../index.php/2018/07/25/07-25-2018-m4-6-near-ensenada/#respond Wed, 25 Jul 2018 20:42:56 +0000 http://www.scsn.org/?p=2835 ]]>
  • 25 Jul 2018 13:17:56 PDT, (31.950, -116.298), depth 15.8km, 32km ENE of Ensenada, B.C., Mexico
  • Aftershocks: so far there have been no aftershocks recorded. Some may be expected in the next few days, the largest expected is approximately 1 magnitude unit smaller than the mainshock. There is a small chance (about 5%) that a larger quake could occur, with the likelihood decreasing over time.
  • Historical seismicity: since our records began in 1932 we’ve had 42 events of M4 or greater within 10km of today’s event, the largest was M6.8 (1956/02/09) and the most recent was M4.1 on 09 Aug 2011.
  • Links for: USGS earthquake page, ShakeMap, DYFI, waveforms.
  • Visit our special reports page for further information on local notable earthquakes.
  • Below are the waveform data associated with this event, as recorded in our Live Seismograms Feed. The closest station to the earthquake shown in the view is CI.SDG in San Diego at approximately 120km from the epicenter.

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    07/10/2018, M3.6 near Ontario ../../index.php/2018/07/10/07-10-2018-m3-6-near-ontario/ ../../index.php/2018/07/10/07-10-2018-m3-6-near-ontario/#respond Tue, 10 Jul 2018 14:30:34 +0000 http://www.scsn.org/?p=2812 ]]>
  • 10 Jul 2018 04:08:37 PDT, (34.010, -117.585), depth 4.3km, 6km SE of Ontario, California
  • Aftershocks: so far (10 Jul 2018, 07:23AM PDT) there have been 5 aftershocks recorded, the largest M2.5 (smallest M0.9). More may be expected in the next few days, the largest expected is approximately 1 magnitude unit smaller than the mainshock. There is a small chance (about 5%) that a larger quake could occur, with the likelihood decreasing over time.
  • Historical seismicity: since our records began in 1932 we’ve had 17 events of M4 or greater within 10km of today’s event, the largest was M5.5 (1990/02/28) and the most recent was M4.4 on 15 Jan 2014.
  • Nearby faults: Red Hill-Etiwanda Avenue fault (10.5 km) and Elsinore fault zone, Chino section (Chino fault) (11.0 km).
  • Links for: USGS earthquake page, ShakeMap, DYFI, waveforms.
  • Below are the waveform data associated with this event, as recorded in our Live Seismograms Feed.The closest station to the earthquake shown in the view is CI.RVR in Riverside at approximately 19km from the epicenter.

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    05/30/2018, M3.8 near Thousand Palms ../../index.php/2018/05/30/05-30-2018-m3-8-near-thousand-palms/ ../../index.php/2018/05/30/05-30-2018-m3-8-near-thousand-palms/#respond Wed, 30 May 2018 19:35:31 +0000 http://www.scsn.org/?p=2783 ]]>
  • 30 May 2018 12:22:05 PDT, (33.924, -116.323), depth 9.5km, 13km NNE of Thousand Palms, California
  • Aftershocks: so far (30 May 2018, 12:33PM PDT) there have been 2 aftershocks recorded, the largest M1.2 (smallest M0.9). More may be expected in the next few days, the largest expected is approximately 1 magnitude unit smaller than the mainshock. There is a small chance (about 5%) that a larger quake could occur, with the likelihood decreasing over time.
  • There were 1 events during the 3 days prior to the earthquake (within a 10 km radius), the largest was M0.6 (2018/05/30).
  • Historical seismicity: since our records began in 1932 we’ve had 88 events of M4 or greater within 10km of today’s event, the largest was M6.1 (1992/04/23) and the most recent was M4.0 on 06 Aug 2010.
  • Nearby faults: unnamed Fault in the Little San Bernardino Mountains (1.4 km), Blue Cut fault zone (Blue Cut fault) (2.2 km), Eureka Peak fault (5.0 km), San Andreas fault zone, San Bernardino Mountains section (North Branch SAF) (6.6 km), Burnt Mountain fault zone (East Wide Canyon fault) (6.8 km), San Andreas fault zone, San Bernardino Mountains section (6.8 km), Indio Hills fault zone (9.2 km), San Andreas fault zone, San Bernardino Mountains section (South Branch SAF) (9.5 km) and Long Canyon fault (10.9 km).
  • Links for: USGS earthquake page, ShakeMap, DYFI, waveforms.
  • Visit our special reports page for further information on local notable earthquakes.
  • Below are the waveform data associated with this event, as recorded in our Live Seismograms Feed.The closest station to the earthquake shown in the view is CI.WWC in Palm Springs at approximately 8km from the epicenter.

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    05/08/2018, M4.5 near Cabazon ../../index.php/2018/05/08/05-08-2018-m4-5-near-cabazon/ ../../index.php/2018/05/08/05-08-2018-m4-5-near-cabazon/#respond Tue, 08 May 2018 13:57:59 +0000 http://www.scsn.org/?p=2711 ]]> A M4.5 earthquake occurred at 4:49 local time this morning (May 8) under the San Bernardino Mountains, near a complex part of the San Andreas fault. Seismologists call this region the “San Gorgonio knot” because so many small faults intersect here and the main San Andreas trace is not clearly defined.

    Historically, this area around Mt. San Gorgonio is the only part of the southern San Andreas fault that produces smaller quakes. Many M3-4 earthquakes have been recorded here. The largest were the M6.0 Desert Hot Springs earthquake in 1948 about 30 miles to the east and the 1986 M5.9 North Palm Springs earthquake that was less than 10 miles east of today’s earthquake.

    The focal mechanism calculated by Caltech and the USGS for this earthquake Moment Tensor Page shows the event happened on a fault that strikes a little north of east-west and that the motion was primarily thrust faulting. This means that the north side moved up and over the lower south side of the fault. This is very similar to the motion we saw in the 1986 North Palm Springs earthquake. (https://authors.library.caltech.edu/48710/.)

    This morning’s M4.5 was felt from San Diego to Los Angeles. More than 10,000 people have reported feeling it at Did you feel it?. The strongest shaking recorded by the instruments is Intensity VI.

    This size earthquake is common in California, happening many times each year somewhere in the state. This is normal activity and has no relationship to the Hawaii eruption.

    Technical information about this earthquake and its aftershocks:

    • 08 May 2018 04:49:34 PDT, (34.017, -116.780), depth 12.9km, 11km N of Cabazon, California.
    • Aftershocks: so far (09 May 2018, 10:40AM PDT) there have been 88 aftershocks recorded, the largest M3.2 (smallest M0.2). More may be expected in the next few days, the largest expected is approximately 1 magnitude unit smaller than the mainshock. There is a small chance (about 5%) that a larger quake could occur, with the likelihood decreasing over time.
    • Plot of seismicity through time, from 0.5 days before the M4.5 Cabazon event to approximately 1.25 days after. Top plot shows cumulative earthquake count against time. Bottom plot shows earthquake magnitude against time, the M4.5 event and M3.2 aftershock are plotted as red stars.
      Map showing the M4.5 earthquake near Cabazon (red star) with foreshocks and aftershocks in a 10km radius shown as circles colored by time (blue = early, red = late) and sized by magnitude. Grey stars labelled by magnitude show historic earthquakes. Grey lines show the mapped fault strands in the San Andreas fault zone.
    • Historical seismicity: since our records began in 1932 we’ve had 46 events of M4 or greater within 10km of today’s event, the largest was M6.0 (1986/07/08) and the most recent was M4.4 on 06 Jan 2016.
    • Nearby faults: San Andreas fault zone, San Bernardino Mountains section (3.0 km).
    • Links for: USGS earthquake page, ShakeMap, DYFI, waveforms.
    • Visit our special reports page for further information on local notable earthquakes.

    Below are the waveform data associated with this event, as recorded in our Live Seismograms Feed.The closest station to the earthquake shown in the view is CI.WWC in Palm Springs at approximately 35km.

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    05/01/2018, M3.7 near San Clemente Is ../../index.php/2018/05/01/05-01-2018-m3-7-near-san-clemente-is/ ../../index.php/2018/05/01/05-01-2018-m3-7-near-san-clemente-is/#respond Tue, 01 May 2018 11:48:01 +0000 http://www.scsn.org/?p=2703 ]]>
  • 01 May 2018 04:22:22 PDT, (32.787, -118.443), depth 8.0km, 10km WSW of San Clemente Is.
  • Aftershocks: so far (01 May 2018, 07:20AM PDT) there have been 3 aftershocks recorded, the largest M3.4 (smallest M2.8). More may be expected in the next few days, the largest expected is approximately 1 magnitude unit smaller than the mainshock. There is a small chance (about 5%) that a larger quake could occur, with the likelihood decreasing over time.
  • Historical seismicity: since our records began in 1932 we’ve had 4 events of M4 or greater within 10km of today’s event, the largest was M5.8 (1951/12/26) and the most recent was M4.2 on 16 Aug 2001.
  • Nearby faults: San Clemente fault zone (San Clemente fault) (11.0 km).
  • Links for: USGS earthquake page, ShakeMap, DYFI, waveforms.
  • Visit our special reports page for further information on local notable earthquakes.
  • Below are the waveform data associated with this event, as recorded in our Li
    ve Seismograms Feed.The closest station to the earthquake shown in the view is CI.RPV in Long Beach at approximately 106km.

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    04/25/2018, M3.9 near Borrego Springs ../../index.php/2018/04/26/04-25-2018-m3-9-near-borrego-springs/ ../../index.php/2018/04/26/04-25-2018-m3-9-near-borrego-springs/#respond Thu, 26 Apr 2018 01:44:49 +0000 http://www.scsn.org/?p=2695 ]]>
  • 25 Apr 2018 18:36:00 PDT, (33.380, -116.298), depth 13.9km, 16km NNE of Borrego Springs, California
  • Aftershocks: so far (26 Apr 2018, 02:27PM PDT) there have been 5 aftershocks recorded, the largest M1.2 (smallest M0.8). More may be expected in the next few days, the largest expected is approximately 1 magnitude unit smaller than the mainshock. There is a small chance (about 5%) that a larger quake could occur, with the likelihood decreasing over time.
  • There were 4 events during the 3 days prior to the earthquake (within a 10 km radius), the largest was M2.5 (2018/04/25).
  • Historical seismicity: since our records began in 1932 we’ve had 41 events of M4 or greater within 10km of today’s event, the largest was M6.0 (1937/03/25) and the most recent was M5.2 on 10 Jun 2016.
  • Nearby faults: San Jacinto fault zone, Anza section (Clark fault) (1.1 km), San Jacinto fault zone, Anza section (5.8 km), San Jacinto fault zone, Coyote Creek section (6.6 km), San Jacinto fault zone, Coyote Creek section (Coyote Creek fault) (6.8 km) and San Jacinto fault zone, Anza section (Buck Ridge fault) (7.0 km).
  • Links for: USGS earthquake page, ShakeMap, DYFI, waveforms.
  • Visit our special reports page for further information on local notable earthquakes.
  • Below are the waveform data associated with this event, as recorded in our Live Seismograms Feed. The closest station to the earthquake shown in the view is CI.WWC in Palm Springs at approximately 60km.

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    04/22/2018, M3.9 near Thousand Palms ../../index.php/2018/04/23/04-22-2018-m3-9-near-thousand-palms/ ../../index.php/2018/04/23/04-22-2018-m3-9-near-thousand-palms/#respond Mon, 23 Apr 2018 01:03:09 +0000 http://www.scsn.org/?p=2683 ]]>
  • 22 Apr 2018 17:46:08 PDT, (33.922, -116.322), depth 8.2km, 13km NNE of Thousand Palms, California
  • Aftershocks: so far (23 Apr 2018, 07:19AM PDT) there have been 7 aftershocks recorded, the largest M2.2 (smallest M0.8). More may be expected in the next few days, the largest expected is approximately 1 magnitude unit smaller than the mainshock. There is a small chance (about 5%) that a larger quake could occur, with the likelihood decreasing over time.
  • Historical seismicity: since our records began in 1932 we’ve had 85 events of M4 or greater within 10km of today’s event, the largest was M6.1 (1992/04/23) – the Joshua Tree earthquake. The most recent event was M4.0 on 06 Aug 2010.
  • Nearby faults: unnamed Fault in the Little San Bernardino Mountains (1.1 km), Blue Cut fault zone (Blue Cut fault) (2.0 km), Eureka Peak fault (5.4 km), San Andreas fault zone, San Bernardino Mountains section (North Branch SAF) (6.3 km), San Andreas fault zone, San Bernardino Mountains section (6.8 km), Burnt Mountain fault zone (East Wide Canyon fault) (7.1 km), Indio Hills fault zone (8.9 km), San Andreas fault zone, San Bernardino Mountains section (South Branch SAF) (9.3 km) and Long Canyon fault (11.1 km).
  • Links for: USGS earthquake page, ShakeMap, DYFI, waveforms.
  • Visit our special reports page for further information on local notable earthquakes.
  • Below are the waveform data associated with this event, as recorded in our Live Seismograms Feed.

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