SCEC Summer Internship Research Diary of

Nathan Earl Robison, EI.

Week of:

Monday, June 29, 1999

Employment with Sage Engineering, a local consulting firm. Full-time work accepted temporarily while waiting for funding (so often the story with science!). Consulting work involves slope stability and hydrology analysis for mine reclamation.

Some progress on Maximum Intensity map. Collection of isoseismal maps has grown to around 80, and the catalog of earthquakes is now over 600. I expect to have a paper prepared by late July and a map including over 800 earthquakes. A strong magnitude dependence seems to emerge from the data - that is, a "threshold acceleration" at which each intensity may occur is much lower for large earthquakes - significantly lower than the relations given by Toppozada and others would suggest.

Monday, July 6, 1999

Continuing consulting work. Several home improvement needs have conflicted with scheduling.

Tentative plans arranged with a respected local seismologist to help with field work for ongoing precarious rock studies, as arranged through my mentor.

Eureka! Data can be exported as formatted text from a spreadsheet in the following format (for example) into AutoCad™ and read into the program by using the Tools>Read Script> command.

circle -10.532,-5.632 .6521

would plot a circle of radius 0.6521 at the x-y coordinate -10.532,-5.632. This means that, with some careful formatting (only one space where one would type "Enter" on the command line) the 600+earthquake data set can be plotted in seconds - this task required some 3 hours during the semester at the inception of this project.

Monday, July 13, 1999

Beginning report to accompany Maximum Intensity Map, submission date will probably be within schedule. The prospect of a co-authored paper with my mentor is very exciting, and we believe that this project may be a worthy contribution to the literature surrounding intensity/acceleration study.

Began to review literature of modern hazard analysis. The increased hanging wall effects documented in thrust and normal fault models, testing, and to some extent experience, is an exciting phenomenon. We are looking into the physics of the phenomenon. Several maps reviewed and compared to the existing database of some 150 precarious or semi-precarious rock locations, looking for possible discrepancies.

Dr. Brune and I have discussed the sites which could significantly benefit from evidence gathered from precarious rock surveys - I expect that the major field work this summer will concentrate on the White Wolf fault hanging wall - construction of several 17-25 km cross-sections showing possible evidence of the upper boundary for horizontal acceleration during the 1952 rupture.

Developed method of measuring a precarious boulders' volume and computing center of gravity. Standard survey equipment - a single prism, electronic distance meter and theodolite total station, and a spreadsheet developed to produce rough finite-element calculations should generate volume calculations with less than 5% error, based on preliminary calculations. A copy of the spreadsheet will be available after it has been tested on several field situations.

Monday, July 20, 1999

Meeting with Dr. Brune and Dr. Rasool Anooshehpoor, the latter a research associate with the UNR Seismology department. Plans for field time the week of July 27th Spent several hours reviewing maps generated by existing precarious rock surveys. Discussion of testing procedures to verify analytical and numerical models for toppling accelerations for precarious and semi-precarious rocks.

Thursday, July 23 - Meeting with Dr. Anderson, discussion of report format, needed analysis, and significant historical earthquakes which do not have well-defined magnitudes assigned to them, but which may be determinant in relatively stable Eastern US regions. Discussion of seismic gaps and their meaning for earthquake prediction - note of several areas in California and Utah, particularly, which may be at risk from accumulated strain in areas bordered by ruptures.

Friday, July 24 - Field time with Dr. Brune, visiting spectacular collection of standing stones, some quite massive (mass > 2000 kg), and some less than 2 km from a known Holocene active normal fault in NW Nevada - on the footwall, as one might expect.

Monday, July 27, 1999

Left mid-day Monday for Palmdale, CA with R. Anooshehpoor. 1.5 days testing precarious rocks in the San Gabriel Mts. 8 rocks tested using pressure gauge and hydraulic jack, strain-guage-based tensometer and force meter (electronic) and cables, scaffolding, and acrobatics as the situations dictated. 15-hr days while in the field: very satisfying. A lot of hiking. Calculations performed in the field from measurements made to estimate volume. Survey equipment not available for more refined measurements, but volumes calculated from geometrically simple shapes: prisms, cones and sections, cylinders, spheres, and the like. Characteristic rock samples (generally low-mica content pegmatitic anorthosite to Quartz monzodiorite) retrieved for density determination.

Wednesday, July 29 - Drove to location of 1952 White Wolf rupture, geology, rockslides, and the significance of hanging wall strong motion control discussed. Obtained permission from private Bear Valley community police to use local private roads for access to precarious rock survey area. Checked on solar charging and recording status of two weak-motion seismometers in the Mojave desert near Saddleback Butte in the Mojave. These instruments will be used in the upcoming LAARS 2 tests to investigate site effects at precarious rock outcrops near the San Andreas. A pack rat had chewed through the wiring of one instrument. We repaired the wire and used dead cactus, stones, and a lot of sand (we slept well that night) to inconvenience the little denizen for future security.

Thursday, July 29 - returned to Reno - in-depth discussion with R. Anooshehpoor on foam model testing and rock model testing, the physics of wave energy concentration, computer modeling of thrust faults, and related subjects.

Monday, August 2, 1999

Meeting with J. Anderson, formatted matrix for exact solution to the 3-equation, 4-unknown data set for relating threshold intensity to acceleration as a function of magnitude. Also discovered "Goal Seek" tool in Excel, which allows for effective, if tedious, iterative optimization of constants. Standard deviation of modeling equations decreased with this method by about 4%. Matrix solution identical - the iteration converged to meaningful values. Plans to add Hawaii and Alaska to Maximum Intensity map: a challenge but a few more very late nights will probably not hurt you at 24 years old.

Wednesday-Friday, August 4-6, travelled to Bishop, CA, arriving at 2am to sleep 3 hours before continuing to LA. Shocked, of course, by traffic but we (my wife Paula, daughter Rosemary, and I) found USC with little pain. Attended SCEC intern colloquium. Exciting and prolonged presentations by interns on their research topics and status. Used presentation style of handouts of produced maps and data analysis and a fellow student as a model to demonstrate precarious rocks and concepts. Also very valuable field trips, particularly Dr. Karl Mueller and geology of blind thrusts and tour of ECI office. Departed 5pm Friday, drive to Tehachapi, CA.

Saturday-Monday, August 7-10, Precarious rock survey in the area of the White Wolf fault, source of the 1952 Kern County (Arvin/Tehachapi) damaging earthquake. Event may be considered a source of insight into the effects of a blind thrust rupture in the LA basin. Very successful field time. Links to photographs of the more spectacular rocks will be forthcoming after development of figures. An unbroken line of rocks (28 precarious or semi-precarious rocks with overturning acceleration estimated in the field to be from 0.14 to 0.49g) from 8-16km back from fault scarp near Arvin found by binocular and hiking. Rosemary assisted. The catalog in MS Excel 2000 format may be downloaded as WWsurveyRocks.xls

Monday, August 9, 1999

Drove to Reno from Tehachapi field time, arriving 11pm. Returned to engineering work the following day. Beginning to compile data gathered from WW fault area, formalizing on spreadsheet (see link above) to calculate positions for map drafting. Necessary 7.5min quadrangles and geologic maps ordered. Toppling accelerations (field estimates) range from 0.14 to 0.49g. Plans to digitize topography, features, and geology and overlay rock locations and a sort of hard-data PSHA map based on estimated toppling accelerations, and for comparison with existing long-return PSHA maps and the results of attenuation relations.

Seismology server account finally granted, but unable to contact network administrator for access to web page servicing. Hope to have a functioning web site by the middle of next week.

Some text development begun for the report to accompany the White Wolf seismic hazard map. Notes in the field transcribed and the fruits of several related publications.

Monday, August 16, 1999

Web page loaded to a local ISP rather than waiting for the UNR seismo lab administrator to return from his first vacation in several years.

Completed gathering earthquake databases for Alaska and Hawaii to generate maximum intensity maps for these states as well. A long process, considering the activity of Alaska. Attenuation relations used for both are the same as those used in California; in Alaska, the heavily faulted and jointed crust and relatively thin cover should prove similar for attenuation of wave energy to California. In Hawaii, the high earthquake activity rate and density of the crust are inconclusive, but the more conservative attenuation relations for the western US are used to avoid exaggeration.

Maps for the White Wolf area have been recieved. Preliminary overview suggests strongly that the distribution of rocks will provide a useful model for seismic hazard analysis in the area. Plans to present findings and a preliminary map to Dr. J. Brune early next week, after he and Dr. Anderson return from professional meetings to begin the Fall semester at UNR.

Classes begin Monday the 23rd. I will be studying Sedimentology and Groundwater Hydrology, as well as an independent study in computer programming under Dr. James Carr with the Geological Engineering department and competing an honors thesis under the mentorship of Dr. Jaak Daemen of Mining Engineering. After four semesters of 20-23 credits each, this 12-credit semester seems very unimposing, and I look forward to ample time to polish and completer the SCEC project for presentation at the SCEC annual meeting.

Monday, August 23, 1999

Meeting with J. Brune, White Wolf distribution and toppling accelerations are very promising. Found and ordered digital line data maps (1:100,000 scale) from USGS for use as a base map to present locations of rocks and the lines of seismic hazard generated by their position and estimated toppling accelerations.

Finished US Maximum Intensity map, including Alaska and Hawaii. Report to accompany the submission for publication will be finished in second draft by the middle of next week. Plan to present map and report to J. Anderson as soon as possible.