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Scientific & Technical Reports - The 2002 Denali Fault earthquake

08-Nov-2002 update

PLEASE NOTE:   IF YOU ARE PLANNING ANY FIELD DEPLOYMENTS TO STUDY THE EARTHQUAKE, WE REQUEST THAT YOU PLEASE CONTACT DONNA EBERHART-PHILLIPS, USGS Anchorage, and make her aware of your plans.  She is in contact frequent contact with DGGS and UAF, hence knows of their plans as well.    Contact information for Donna:

Donna Eberhart-Phillips, USGS Anchorage (907) 786-7019;  (907) 786-7425 fax deberhart@usgs.gov 

More detailed information follows under the following headings.

1)    Geologic plans

2)    Preliminary geologic observations

3)    Geotechnical observations

4)    Seismological observations/instrument deployments

5)    Stress transfer modeling

6)    Geodetic observations

7) Remote Sensing

8) Gravity and Aeromagnetic

9)    InSAR coverage looks very promising

10)    Far distance effects of the seismic waves


GEOLOGIC PLANS


  PRELIMINARY GEOLOGIC OBSERVATIONS

From Peter Haeussler

I just got a call from Tim Dawson and Brian Sherrod. They found the westward extent of the rupture to be at: 63 deg, 31.744 min, 147 deg, 09.468 min. Our fieldwork the other day put the SE extent of the rupture at: 62 deg 19.965 min; 142 deg 34.689 min. Thats about 273 km, or 164 miles of fault rupture!

From Landslide group (Jibson, Harp, Kieffer)-

Expected broad region of landslides, but didn't see it. One valley away,
and there's much less. They all said this was unlike any other earthquake

Flew west from Black Rapids Gl.

In area of 6.7 earthquake, saw three large rockfalls. Possibly from the
earlier event. I'm not sure we were able to travel to where they went.

From Dennis Trabant (WRD glaciologist, Fairbanks) -

Also noted landslides are basically only along the fault valley walls.
Found a keystone graben in snow just E of summit of Coney Mtn, on S. side
of Canwell Glacier.

From Brian Sherrod, Tim Dawson -

Found the W end of the surface rupture as reported yesterday. Traveled E of
the Richardson highway and measured offsets of about 5 m in a couple of
places, and about 7 m in another. They indicated the Plafker-Rubin-Sieh
group worked a bit further E (but perhaps W of the Tok Cutoff?) and found
similar magnitude offsets.


GEOTECHNICAL OBSERVATIONS/PLANS


SEISMOLOGICAL OBSERVATIONS/INSTRUMENTATION DEPLOYMENTS

From Lucy Jones, USGS Pasadena

The rate of aftershocks to the Denali earthquake have been analyzed by
standard methods to determine the parameters in the Gutenberg Richter
relation and in Omori's Law. The data used is the catalog of aftershocks
of magnitude 4.2 and greater determined by NEIC. Enough aftershocks have
been processed to have reasonable estimates of the aftershock parameters
and their error bars.

values of these parameters have been determined previously for many
Californian aftershock sequences. Statements about the rate of aftershocks
in the Alaskan sequence are with respect to to what we have recorded
previously in California. Compared to the California average, this
sequence:

- is much smaller than average. The rate of aftershocks is expressed
relative to the mainshock magnitude. This sequence is as low as any
previously recorded in California, when expressed as delta magnitude.
However, the methodology assumes a scaling with magnitude that has not been
tested for very large earthquakes.

- has a higher b-value than average so more small aftershocks and fewer big
ones

- is decaying somewhat more rapidly than average

It is interesting to compare this sequence to that of the foreshock for
which we have a more complete catalog. The foreshock also had a low
productivity and high b-value but decayed less rapidly.

The best estimate of the parameters are:

Foreshock Mainshock CA generic + S.D.
a -3.45 ± .64 -3.85 ±.73 -1.76 ± .6
b 1.20 ± .16 1.32 ± .20 0.90 ± .13
p 0.88 ± .10 1.26 ± .32 1.08 ± .2

(a is the exponent of the productivity so a change in a of one unit
represents a tenfold change in the number of aftershocks. The b-value is
the exponent in the Gutenberg Richter relationship. The p-value is the
decay constant in Omori's Law.)

We estimate the probability of future aftershocks using a Bayesian
estimates of the parameters. The Bayesian analysis uses the CA generic as
the a priori values and this sequence as the a posteriori. The
probabilities are thus based on values between the generic and specific. It
is about a 50-50 chance that we have already seen the largest aftershock
(M5.8). We would expect 4-5 more M5 aftershocks in the next month.
The probability of a M6 in the next month of 1 in 4. If we used the
parameters in the above table directly, we would get even lower
probabilities.


STRESS TRANSFER MODELING


GEODETIC OBSERVATIONS


REMOTE SENSING


REGIONAL GRAVITY AND AEROMAGNETIC DATA


INSAR COVERAGE LOOKS VERY PROMISING


FAR DISTANT EFFECTS OF THE SEISIMIC WAVES

Triggered Seismicity

Alaska Quake Seems to Trigger Yellowstone Jolts (11/4/2002)

From: Seth C Moran, University of Alaska, Fairbanks-

John Sanchez (University of Alaska Fairbanks student) and I have looked through waveforms from all AVO networks for ~1 hour after the mainshock, and have found candidates for triggered seismicity at only Spurr and Katmai. Here is a summary of what we saw for each network:

Wrangell (281 km SE of epicenter): Nothing of note (clipping lasts 16 minutes, records very noisy with aftershocks, so not a positive negative)

Spurr (368 km SW of epicenter): 1 local earthquake ~14 min after mainshock arrival, shows up clearly on several stations (22:27). In addition, there are many high-frequency waveforms that appeared on one station (CP2) as clipping died down, several of which looked earthquake-like. However, it is likely that these are distortion effects and/or cross-talk, as other stations on the network were still clipping.

Redoubt (458 km SW of epicenter): Nothing of note

Iliamna (511 km SSW of epicenter): Nothing of note

Augustine (586 km SSW of epicenter): Nothing of note

Katmai (720 - 755 km SSW): At least two events show on only one station 3-5 minutes after mainshock arrival (22:18 and 22:20). One event shows on several stations (22:33)

Aniakchak (966 km SSW): Nothing of note

Veniaminof (1070 km SSW): Nothing of note Pavlof (1230 km SW): Nothing of note

Shishaldin (1367 km SW): Nothing of note

Westdahl (1414 km SW): Nothing of note

Akutan (1500 km SW): Nothing of note

Makushin (1558 km SW): Nothing of note Great Sitkin (2105 km SW): Nothing of note

Kanaga (2164 km SW): Nothing of note

We have previously seen triggered earthquakes only at Katmai in association with several M ~7 events that occurred nearby (115 - 160 km). Since dynamic forces should have been large enough to trigger earthquakes at Cook Inlet and Katmai volcanoes, the apparent absence of triggered events at all AK volcanoes except Spurr and Katmai suggests there is something inherently different about Katmai (perhaps the size of geothermal systems?) that makes it much more prone to triggering than other AK volcanoes. The relative absence of triggered earthquakes is also striking in comparison to the triggered seismicity observed at Yellowstone in particular, as well as Mammoth Mountain and other places in the Lower 48.

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