There was a swarm of seismic activity near Honey Lake a couple of days ago. I was stage managing at Reggae on the River, so missed the chance to write about this when it happened. Here is the USGS website for this M 4.5 earthquake.
Here is my interpretive map that shows the epicenter, along with the shaking intensity contours. These contours use the Modified Mercalli Intensity (MMI) scale. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
I also include the MMI contours from the M 5.1 earthquake near Lake Pillsbury. Here is my earthquake report for that M 5.1 earthquake. Compare the MMI contours for these two earthquakes. The Lake Pillsbury M 5.1 earthquake was ~19 km depth and the M 4.5 Honey Lake earthquake was ~7 km depth. Think about the factors that govern how strongly an earthquake is felt at the ground surface. Why does the M 4.5 earthquake, the smaller magnitude earthquake, have larger ground motions at Earth’s surface?
I plot the moment tensor for this earthquake and I interpret this earthquake to be a northwest striking right lateral strike-slip earthquake. This is based upon the mapped faults in the region and their sense of motion, which is synthetic to the San Andreas fault system to the west. I used this kml to make this map.
The San Andreas fault is a right-lateral strike-slip transform plate boundary between the Pacific and North America plates. The plate boundary is composed of faults that are parallel to sub-parallel to the SAF and extend from the west coast of CA to the Wasatch fault (WF) system in central Utah (the WF runs through Salt Lake City and is expressed by the mountain range on the east side of the basin that Salt Lake City is built within). There was a recent earthquake between the San Andreas and Maacama faults in August of 2016 and an earthquake series along the Bartlett Springs fault system on 2016.08.10. The three main faults in the region north of San Francisco are the SAF, the MF, and the Bartlett Springs fault (BSF). The SAF, MF, and BSF are all right lateral strike-slip fault systems.
The major strike slip fault systems that extend along the east side of the Sierra Nevada mountains include the Eastern California Shear Zone (ECSZ, in the south) and the Walker Lane (WL, in the north). The Honey Lake fault system is part of the northern terminus of the Walker Lane and may eventually reveal how Pacific/North America relative plate motion extends westward to the Pacific plate. The ECSZ and WL delineate the eastern boundary of the Sierra microplate.
I include inset maps, from upper left, clockwise.
- I placed a moment tensor / focal mechanism legend in the upper right corner of the map. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely. Based upon the proximity to the Honey Lake fault system, I interpret the M 4.5 earthquake as a right-lateral strike-slip earthquake.
- I include a map from Hunter et al. (2011) that shows the plate boundary scale tectonics and an inset with details of active faulting in the region. This map shows the Mohawk Valley fault zone that is also highlighted in the interpretive map below.
- I include a map from Gold et al. (2014) that also shows the regional active faults related to the Walker Lane.
- I include a map from Turner et al. (2008 ) that show some faults in the region that were evaluated for slip rates by the authors. These authors examined the slip rate and paleoseismic history by evaluating an offset natural stream bank. They interpret at least four surface-rupturing earthquakes during the past 7025 calendar years. Interevent times range from 730 to 990 years. They calculate a minimum slip rate for the Honey Lake fault of 1.7 ± 0.6 mm/yr.
- I include a map that shows the epicenters from the last 30 days in relation to Honey Lake and the faults that are included in the USGS Active Fault and Fold Database.
These are the USGS websites for the larger magnitude earthquakes plotted in the map above.
- 2016.08.04 M 4.5 04:55:35 UTC
- 2016.08.04 M 4.0 04:58:32 UTC
- 2016.08.04 M 2.8 05:11:34 UTC
- 2016.08.04 M 2.5 05:45:07 UTC
- 2016.08.04 M 2.2 06:40:07 UTC
- 2016.08.04 M 3.3 10:13:52 UTC
- 2016.08.04 M 2.0 15:55:23 UTC
Below are the two attenuation with distance plots for the M 5.1 and M 4.5 earthquakes plotted in my interpretive poster above. These show how the ground motions attenuate (get absorbed and diminish) with distance from the earthquake.
- The M 4.5 earthquake (6.9 km depth).
- The M 5.1 earthquake.
Here is the Hunter et al. (2011) map. I include the figure caption as a blockquote below.
(a) Generalized location map showing the Walker Lane–eastern California shear zone (ECSZ) in relation to the Basin and Range Province, the Sierra Nevada microplate, and the San Andreas fault system, as well as relative motions and rates. (b) Generalized fault map of the northern Walker Lane: PF, Polaris fault; DVFZ, Dog Valley fault zone; MVFZ, Mohawk Valley fault zone; GVF, Grizzly Valley fault; HLF, Honey Lake fault; WSF, Warm Springs Valley fault; PLF, Pyramid Lake fault; OF, Olinghouse fault; and CL, Carson lineament. Barbed arrows show relative motion of strike-slip faults, and black dots shows down-thrown side of normal faults. Parts (a) and (b) are modified from Faulds and Henry (2008 ).
Here is the Gold et al. (2014) map. I include the figure caption as a blockquote below.
Map of the northern Walker Lane study area and regional strike-slip and normal faults, simplified from the U.S. Geological Survey, Nevada Bureau of Mines and Geology, and California Geological Survey , Faulds and Henry , the California Department of Water Resources , Saucedo and Wagner , Hunter et al. , Gold et al. [2013a, 2013b], Olig et al. , and our mapping using lidar data and field observations. Abbreviations: CL, Carson Lineament; DVF, Dog Valley fault; ETFZ, East Truckee fault zone; GVF, Grizzly Valley fault; HLF, Honey Lake fault; HSF, Hot Springs fault; IVF, Indian Valley fault; MVFZ, Mohawk Valley fault zone; OF, Olinghouse fault; PF, Polaris fault; PLF, Pyramid Lake fault; and WSVF, Warm Springs Valley fault. Arrows indicate relative direction of strike-slip fault movement. Bar and ball indicates downthrown block of normal faults. Star depicts location of Sulphur Creek site.
Here is the Turner et al. (2008 ) map. I include the figure caption as a blockquote below.
Location of (a) the northern Walker Lane (shaded gray) with respect to the Pacific plate (denoted PP), the San Andreas fault (denoted SA), the North American plate (denoted NAP), the Sierra Nevada, and the Basin and Range province. Plate velocity (∼50 mm=yr) is for the Pacific plate relative to stable North America. Measured geodetically, the Northern Walker Lane is accumulating about 6 2 m=yr of relative right-lateral motion. (b) The Honey Lake fault zone. Strike-slip faults are black and normal faults are white. The Honey Lake (denoted HL), Pyramid Lake (denoted PL), and Winnemucca Lake (denoted WL) subbasins of Lake Lahontan and Lake Tahoe (denoted LT) are labeled. Faults are simplified and generalized from the USGS (2006), and shaded relief generated from 3′ SRTM data are courtesy of NASA/ NGA/USGS.
There was a M 3.8 earthquake along Lake Almanor in March of 2015, near a swarm from 2013 (with an earthquake of M = 5.7). Here is my earthquake report for that swarm. This seismicity is probably related to the Indian Valley fault. The Indian Valley fault is at the northern end of the Mohawk Valley fault system. We will be taking a look at this fault system (and the sedimentary/stratigraphic history) for the 2015 Pacific Cell Friends of the Pleistocene field trip. The Mohawk Valley fault system is probably the northern extension of the Walker Lane. The Walker Lane is the northernmost extension of the east-of-the-Sierra-Nevada-mtns part of the plate boundary between the North America and Pacific plates (the most well known part of this plate boundary is the San Andreas fault). We looked at the Walker Lane for the 2010 Pacific Cell Friends of the Pleistocene field trip. We looked at faulting in the Lake Tahoe region for the 2012 Pacific Cell Friends of the Pleistocene field trip.
Here is a map showing the swarm from 2013, as well as the location of today’s M 3.8 earthquake. All orange dots represent earthquake epicenters from the year of 2013. On the map I have placed the moment tensors for the M 5.7 and M 3.8 earthquakes. The Indian Valley fault is shown in orange. I extended this fault (as a red dashed line) to where it may exist, based upon the recent seismicity. All the other lines are from the USGS fault and fold database. Anyone can use these fault data and they are downloadable here.
As Tom Sawyer of Piedmont Geosciences stated, “Yes, the Lake Almanor basin is a pull apart basin resulting from a releasing bend between the northern Mohawk Valley-Indian Valley fault system and the southern Hat Creek graben. See 1995 Pacific Cell FOP guidebook for more details.” More can be found on Sawyer’s page here.
- Gold, R., Briggs, R.W., Personius, S.F., Crone, A.J., Mahan, S.A., and Angster, S.J., 2014. Latest Quaternary paleoseismology and evidence of distributed dextral shear along the MohawkValley fault zone, northern Walker Lane, California in Journal of Geophysical Research, v. 119, 5014-5032, doi:10.1002/2014JB010987
- Hunter, L.E., Howle, J.F>, Rose, R.S., and Bawden, G.W., 2011. LiDAR-Assisted Identification of an Active Fault near Truckee, California in BSSA, v. 101, no. 3, p. 1162-1181, doi: 10.1785/0120090261
- Turner, R., Koehler, R.D>, Briggs, R.W., and Wesnousky, S.G., 2008. Paleoseismic and Slip-Rate Observations along the Honey Lake Fault Zone, Northeastern California, USA in BSSA v. 98, no. 4, p. 1730-1736, doi: 10.1785/0120070090