Sunday, August 28, 2011

USGS real time stream gages and Hurricane Irene effects of streamflow

The US Geological Survey real time stream gages are nicely reflecting the passage of high precipitation associated with Hurricane/Tropical storm/depression Irene: The dots on the map show a general view of the state of flow and many black ones indicating high flow are in the northeast. (USGS Hurricane Irene resources).

If you click on a state (e.g., Pennsylvania) you can zoom in and then click on a particular gage to see the current flow state and its change with time (hydrograph) and build your own graphs, etc.

Here is the page for the Conestoga River at Lancaster, PA which at least right now (Sunday afternoon August 28, 2011) is on the steep rising limb of the hydrograph:

Location is here at this link

This is a critical USGS function that is under threat of severe reduction due to budget cuts.

I noticed that sometimes you have to reload a few times or just wait for the main map to appear. I don't know if they are getting heavy loads due to public interest or what is going on.

Hat tip to Michelle Cooke for this idea.

Tuesday, August 23, 2011

M5.9 earthquake in Virginia, August 23, 2011

A moderate earthquake occurred today in Virginia (about 66 km NW of Richmond Virginia). It is listed as M5.9 by the USGS and was widely felt in the northeast and mid Atlantic region.

Here is the main USGS site on the event: It looks like it was a NNE-trending reverse faulting mechanism (makes some sense with the geologic fabric and the compression directions in the eastern US).

UNAVCO Community Event Response to the 23 August 2011, Mw=5.8 Virginia Earthquake

Watch the event propagate through the USArray: USArray Ground Motion Visualization

Here is a nice NY Times article with information about the damage, a comparison of the felt effects from this event a similar-sized 2004 California earthquake (Parkfield), and a map of historic events in the eastern US (last big event was 5.4 in New Hampshire in 1940).

Watch the Did You Feel It page to see people report their sensation of the event and where.

Here is a short comment about the difference in attenuation between the east and west of North America.

It looks like it occurred within the Central Virginia Seismic zone which is an area that has produced small and moderate events in the past and is noted as a zone of somewhat increased earthquake hazard by the USGS. Note that there was an M4.5 in this area in 2003 (December 9). It was also widely felt.

Note that this was a tie for the largest earthquake recorded in Virginia: Giles County, Virginia 1897 05 31 18:58 UTC Magnitude 5.9

Here it is relative to historic seismicity. Click on link to see it broader with explanation (from USGS OFR 2006-1017):

from but is derived from the USGS Open File report 2006-1017 below).

Here is a nice map and commentary from Virginia Tech on the Central Virginia Seismic zone.

Social media will be an important channel for people to communicate about this event:
Here are a few youtube links:
Earthquake Virginia Auto Repair Shop Collapses G&C
DC / Virginia Earthquake Aftermath

Wikipedia site is accumulating contributions:

Here it is recorded at Arizona State University (thanks John West):

Here are a few other links I just came up with:
Major earthquakes in Virginia (from Virginia Division of Geology and Mineral Resources)
Earthquakes in Virginia and Vicinity 1774 - 2004 (USGS Open File Report 2006–1017) (big file and takes a while to download)
Virginia Earthquake Information from the USGS

IRIS Event plot suite

Tectonic Setting of the August 2011 Virginia Earthquake (Stein, et al.)

Latest update: 19:05 Arizona time August 29, 2011

Monday, August 8, 2011

Wallace Creek: New radiocarbon results and slip rate estimates of the San Andreas Fault in the Carrizo Plain

Our team along with Sinan Akciz and Lisa Grant-Ludwig from UC Irvine just finished a SCEC-supported project to re excavate a few of the trenches from the now famous work published as Sieh and Jahns, 1984 at Wallace Creek. While the slip rate of the San Andreas Fault has been well established at about 36 mm/yr from that work, it is only constrained by a few radiocarbon dates. With our experience working in the area and the enhanced capabilities of the W. M. Keck Carbon Cycle Accelerator Mass Spectrometry Laboratory  at UC Irvine, we proposed that it was time to revisit the ages of the main offset channel at Wallace Creek.

Aerial view of open excavations (photograph by Wendy Bohon, ASU)

View Larger Map

The effort was highlighted in a local newspaper: .

Here is our SCEC abstract that was just submitted (the title of this blog entry is the same):

Revisiting Wallace Creek: New radiocarbon results and slip rate estimates of the San Andreas Fault in the Carrizo Plain

S.O. Akciz, D.E. Haddad, W. Bohon, L. Delgadomendes, G. Marliyani, B. Salisbury, T. Sato, L. Grant Ludwig, J R. Arrowsmith

Sieh and Jahns (1984) determined the slip rate of the San Andreas fault (SAF) at Wallace Creek in the Carrizo Plain, and thereby provided an anchor for nearly all data-driven models of the southern San Andreas fault behavior. Their landmark study has been referenced hundreds of times and is a critical constraint in many related studies and in hazard estimates for the south-central SAF. Slip rate estimates at Wallace Creek (33.9±2.9 mm/yr) and at Van Matre Ranch site
(29.3-35.6 mm/yr; Noriega et al., 2006) agree well within measurement uncertainty, and with the 30–37 mm/yr velocity gradient across the SAF from decadal timescale geodetic measurements (Schmalzle, et al., 2006). Surprisingly, only a few detrital charcoal samples (9 samples at VMR, 8 samples at Wallace Creek) have been used to provide the absolute geochronological constraints. At a third site, Phelan Creeks, located ~ 2.5 km SE of Wallace Creek, 23 trenches were opened and over 400 charcoal samples were collected (Sims et al., unpublished data) to provide additional slip rate constraints, but the detailed study was never published.

New paleoseismologic investigations at the Bidart Fan site, ~5 km SE of Wallace Creek, indicate that southern SAF in the Carrizo Plain has apparently ruptured, on average, every 88 years (45-144 yr for individual intervals) between ~A.D. 1350 and 1857 (Akciz et al., 2010). B4 LiDAR (light detection and ranging) data analysis by Zielke et al. (2010) also found that only ~5.5 m of slip occurred along the SAF in the Carrizo Plain in 1857 and at least since ~A.D. 1400, and none of the earthquakes generated displacements larger than 5 meters (Grant Ludwig et al., 2010).

Slip per event and earthquake timing constraints can be tested against slip rate information to assess the steadiness of slip. Therefore, these new data and the geochronological limitations of the published slip-rate studies emphasize the need to improve, if not confirm, the existing slip-rate estimates by providing additional geochronological constraints. In August, 20111, we re-excavated T7 and T11 from Sieh and Jahns' study, photologged the trench walls (1:10) and collected a total of 30 new detrital charcoal samples from different stratigraphic layers from both of the trenches. Trench logs and radiocarbon results will be presented.

Akciz, S.O., Grant Ludwig, L., and Arrowsmith, J R., 2009, Revised dates of large earthquakes along the Carrizo section of the San Andreas Fault, California, since A.D. 1310±30. Journal of Geophysical Research-Solid Earth, v. 114, B01313-6841.

Akciz, S.O., Grant Ludwig, L., Arrowsmith, J R., Zielke, O., 2011. Century-long average time intervals between earthquake ruptures of the San Andreas fault in the Carrizo Plain, California: Geology, v. 38, p. 787-790.

Grant Ludwig, L., Akciz, S.O., Noriega, G. R., Zielka, O., Arrowsmith, J R., 2010. Climate- Modulated Channel Incision and Rupture History of the San Andreas Fault in the Carrizo Plain: Science, 327, 5969, p. 1117-1119.

Sieh, K. E., 1977, Late Holocene displacement along the south-central reach of the San Andreas Fault, Ph.D. dissertation, Stanford University, Stanford, California, 219 pp.

Sieh, K.E., and Jahns, R.H., 1984, Holocene Activity of the San-Andreas Fault at Wallace Creek, California: Geological Society of America Bulletin, v. 95, p. 883-896.

Zielke, O., Arrowsmith, J R., Ludwig L G., Akciz, S.O., 2010. Slip in the 1857 and Earlier Large Earthquakes Along the Carrizo Plain, San Andreas Fault: Science, 327, 5969, p. 1119-1122.