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Scientific & Technical Reports - The 2002 Denali Fault earthquake

13-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


GEOTECHNICAL OBSERVATIONS/PLAN

From Christina Neal on afternoon of 11/12:

Aeromap launched today - the weather from Paxon was reported to be
beautiful! I hope to have word from Aeromap later today about actual coverage. Cross your fingers!

To recap the plan as I understand it:

1 - Their first acquistion was to be for ~24K worth of 1:6000 imagery of the portion of the fault identified by early field crews as priority one in ABTill's email of 11/6:

"The swath covers the fault trace from the Susitna Glacier, across the Richardson Highway, Tok cutoff road, and down the rupture trace of the Totschunda fault east of the Tok cutoff road. We have asked them to start at the SE end of the line (near Blue Lake in the Nabesna quad) and fly northwestward. They have Peter's GPS data and maps prepared by Peter with the fault trace on them for navigation purposes."

2 - I have verbally notified Aeromap that an additional ~24K is available to complete 1:6000 coverage ASAP (tomorrow?). We will need input and GPS coordinates and map information from the field crews to create the mission plan. I HAVE ASKED DONNA TO RELAY TO PETER OR OTHERS RETURNING FROM THE FIELD TODAY/TONIGHT TO BE READY TO HELP. I suggest we go over to the Aeromap office tomorrow morning at 0830 to look at maps together, see what they obtained today, and give them guidance on the next flight. I have asked them to be prepared to fly tomorrow. From talking with Dave Schwartz, additional key priorities to be sure we cover:

Zone of intersection Susitna/Denali Faults, extent of Susitna
Zone of intersection Denali and Totschunda Faults

3 - Depending on what money remains from the ~50K John Filson has committed, we may then proceed with the smaller scale (1:25,000) landslide focussed air photos (Aeromap apparently gave a quote of ~11K on Friday, but I do not know the specific request). HAS ANYONE FROM THE LANDSLIDE GROUP COMPILED A FLIGHT TRACK WITH GPS COORDINATES AND SPECIFICATIONS FOR THIS REQUEST?

4 - What has become of Kerry Sieh and Charlie Rubin - do they still want to chip in ~10K for coverage?

Guidance and input welcome.

From Jill McCarthy:

Below is a copy of the e-mail that Rex Baum sent regarding the Landslide request (this e-mail to FEMA but the details define the desired flight area). The 1:25,000 scale was chosen to provide about a 5-km-wide swath image, centered about the fault trace. It was my impression that AeroMap might also have been given the same basic instructions

To follow up on our earlier conversation, in the event that FEMA does become involved in acquiring any imagery, we are wanting to obtain high-resolution imagery (1:25,000 scale aerial photography or equivalent) along a 5-m wide trace of the Denali Fault from where it crosses Alaska State Highway 3 (N63.45, W148.83) east to where the trace of the Totschunda Fault crosses the Chisana River (N62.00, W142.20). This curving trace of the fault between these coordinates extends slightly beyond the heavy green and red lines in the maps at the following location: http://neic.usgs.gov/neis/bulletin/02_EVENTS/EQ_021103/alaska_hazards.html

If you need any additional information, please contact me.

From Christina Neal 11:30am 11/13:

Good news!
1 - Yesterday was gorgeous, Aeromap reports acquisition of images at 1:6000 for ~the western half of the main rupture from the West Fork Glacier margin eastward to the Slana River intersection with the main fault. By my eye this is about half the mapped rupture zone. They could not proceed east due to clouds, and they returned to ANC about 5 pm.

2 - Today the weather looks to be flyable in the west and poor in the east. The intial plan is to fly the newly identified Susitna splay at 1:6000 and then make a weather call and either begin the 1:25,000 sequence or beeline back to the eastern end to attempt to complete the lower altitude segment southeastward down the Totschunda.

IMPORTANT: Please verify that the area of acquisition for the 1:25,000 photos is as follows from a Rex Baum email: high-resolution imagery (1:25,000 scale aerial photography or equivalent) along a 5-m wide trace of the Denali Fault from where it crosses Alaska State Highway 3 (N63.45, W148.83) east to where the trace of the Totschunda Fault crosses the Chisana River (N62.00, W142.20). This curving trace of the fault between these coordinates extends slightly beyond the heavy green and red lines in the maps at the following location:

http://neic.usgs.gov/neis/bulletin/02_EVENTS/EQ_021103/alaska_hazards.html

3 - Film from yesterday has been sent for processing; they should have it back on Friday.

4 - I need to work with admin to amend our purchase order for a higher amount and may need Menlo Park assistance if paperwork must be elevated to a regional center.


SEISMOLOGICAL OBSERVATIONS/INSTRUMENTATION DEPLOYMENT

From Art Frankel:

I've done an initial look at the strong-motion records for the M7.9 earthquake and done some modeling of the waveforms. The records I have are for Fairbanks (NSMP), Anchorage (NSMP and UA/ANSS), Valdez (NSMP) and two portable instruments deployed near the Park Highway (west of the M6.7 epicenter) by the Geophysical Institute people. Peak accelerations are modest: about 10%g for the portables (distance from epicenter of 60-70 km), about 8%g at Fairbanks (150 km distance), generally about 1-2%g at Anchorage, about 1-3%g in Valdez. The similar accelerations for the portables compared to Fairbanks may be partly due to rupture propagating away from them. There may also be site response issues.

Three major sub-events can be seen in the displacement waveforms of the strong-motion records, although the third one is only clear at Valdez. I modeled the waveforms of the first sub-event using a thrust fault with a strike east-northeast. I located the second sub-event using the relative arrival times in the records. The second sub-event is located about 80 km east of the hypocenter. This is the location where the surface strike slip offset averages about 4.5m, according to Dave Schwartz's information. The waveforms for the second sub-event appear to be consistent with a right-lateral strike slip mechanism. The third sub-event is only clear on Valdez. Assuming a rupture velocity of 3 km/sec puts this sub-event about 170 km east of the hypocenter. This would place this third sub-event near where the largest surface offset is observed. Of course, all these distances are distances to the centroid of energy release for these periods, which are about 10-20 sec. The sub-events are separated by about 30-40 sec in time in the records, depending on the azimuth of the stations. Of course, there may be other "sub-events" at different periods that are not obvious in the displacement records and there is slip occurring between the sub-events.

These findings are similar to those from the teleseismic inversion, although the second sub-event is quite distinct on the strong-motion records and not so obvious on the teleseismic inversion I've seen. Looking at the records from Valdez, which is approximately equidistant from the three sub-events, the highest horizontal accelerations are associated with the first two sub-events. The azimuthal distribution of the available strong-motion stations is not optimal. It will be very important to see the records from the pipeline, in the forward directivity direction for some of the rupture.


STRESS TRANSFER MODELING


GEODETIC OBSERVATIONS

From Fred Pollitz:

Denali Deployment (PDF)


REMOTE SENSING


REGIONAL GRAVITY AND AEROMAGNETIC DATA


INSAR COVERAGE LOOKS VERY PROMISING


FAR DISTANT EFFECTS OF THE SEISIMIC WAVES

 

 
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