evaluation of county, california

State of California Business, Transportation and Housing Agency M e m o r a n d u m Flex your power! Be energy efficient!

To: MR. TOM OSTROM Date: February 13, 2013 OFFICE OF EARTHQUAKE ENGINEERING CHIEF

File: 08-SBd-330, PM R29.60 0000001016 6SSCN

Highland Avenue OC Bridge No. 54-1086

Attention: Mr. Mark Yashinsky

From: DEPARTMENT OF TRANSPORTATION DIVISION OF ENGINEERING SERVICES Materials Engineering and Testing Services and Geotechnical Services

Office of Geotechnical Support – Geotechnical Instrumentation Subject: Evaluation of Fault Rupture Potential, Highland Avenue Overcrossing, Br. No. 54-

1086, San Bernardino County, California

“Caltrans improves mobility across California”

SUMMARY

Highland Avenue Overcrossing (OC), Br. No. 54-1086, is more than 300 ft south of the main trace of the Caltrans-active San Andreas Fault (San Bernardino South Branch). Since the fault could not be definitively located in the field during this evaluation, an analysis was performed assuming the mapped location of the main trace and a secondary trace beneath the OC. A design value of 2-1/2 feet of right lateral offset on the N79W trending fault anywhere beneath the OC was determined. Please inform us if this structure cannot withstand this movement and you want to consider further work to refine the value/location. INTRODUCTION This evaluation was prepared as part of the statewide evaluation of fault rupture potential at Caltrans bridges. Caltrans’ policies regarding fault rupture at bridges are described in Memo to Designers (MTD) 20-10. Caltrans requires a fault rupture evaluation if a bridge is located within an Alquist-Priolo Earthquake Fault Zone (EFZ) or within 1,000 feet of an un-zoned fault 15,000 years or younger in age. Highland Avenue OC is situated within the EFZ established in 1974 for the Harrison Mountain 7-1/2’ Quadrangle; therefore a fault evaluation was required.

MR. TOM OSTROM Highland Avenue OC #54-1086 February 13, 2013 Fault Rupture Potential 0000001016 6SSCN


An initial estimate of potential offset was based on an analysis developed by the Division of Research and Innovation in collaboration with Geotechnical Services, using methods presented in Petersen et al (2011) and Abrahamson (2008). Both a deterministic fault displacement hazard analysis (DFDHA) and a probabilistic fault displacement hazasrd analysis (PFDHA) were performed using magnitude, slip rate (for PFDHA), mapping and base map errors, and likelihood of secondary fault traces. If the main trace of the San Andreas Fault (San Bernardino South Branch) crossed beneath the OC, the expected displacement at the OC would be about 20 feet deterministically or 15 feet probabilistically. Since the fault is well-studied at this latitude we used the probabilistic value. Mark Yashinsky and Fadel Alameddine reviewed the bridge plans and determined the OC could not withstand the estimated 15 feet of displacement without modification. Therefore additional work, documented herein, was performed to better define the fault location and to address the possibility of additional fault strands crossing beneath the OC. Highland Avenue Overcrossing was built in 1993 and is a single span bridge 143 feet long and 80 feet wide, supported on steel “H” piles. FAULT RUPTURE EVALUATION The evaluation consisted of: 0

Review of existing data, Review of aerial photography,

Field reconnaissance.

The evaluation reached the following conclusions:

The mapped fault nearest to the OC is the main trace of the San Andreas Fault (San Bernardino South Branch),

It is unlikely that the main fault trace crosses beneath the OC

Secondary traces may cross beneath the OC.

Review of existing data The fault located nearest the OC is the Caltrans-active San Andreas Fault (San Bernardino South Branch). Several types of existing evidence suggest that while the main



trace of the San Andreas Fault (San Bernardino South Branch) does not cross beneath the OC, secondary traces (inactive or low activity?) may be present between the main trace and the OC, and may actually cross beneath the OC. 1. Numerous fault evaluation investigations have been performed in this area for the AP

EFZ program (Figure 1) including several near the OC that were used for evaluating fault rupture at the OC. A 1997 study by Leighton and Associates included excavation of two trenches (T3 and T4) 17-37 feet deep into Pleistocene materials and would have likely encountered any active faults south of the main trace near the OC (Figure 3). No faulting was observed by the consultants. The City of San Bernardino reviewer, Floyd Williams, observed the T3 and T4 trenching as well as trenching in the bed of City Creek 100-200 ft northeast of the site, where the fault reportedly reached the surface. Williams commented that, “This strong expression of active faulting to the north of the subject property [at City Creek] strongly suggests that if faulting had cut across the property it would be evident in Trench T-3 or T-4. Additionally he noted that work done to the northwest of the site for the Walmart site revealed no faulting as well. An earlier study was conducted in 1977 by Gary Rasmussen and Associates on the property southwest of the OC. A trench excavated on that site also failed to reveal faulting in older material. A building exclusion zone was created northeast of the site near the OC because although the report indicated the main trace was likely 400-500 feet to the northeast (and correspondingly 300-400 feet northeast of the OC) since they did not extend the trench that far north they could not conclusively state this. Trenches on this site would not encounter faulting that would likely affect the OC because of the site’s location to the southwest.

2. A research study undertaken in 1995 just north of the OC in the channel of City Creek (McGill et al, 1998) likely overlapped with the project observed by Williams (Figure 2). As part of their work, a trench excavated by a consultant was re-opened (Figure 3). Professor McGill was contacted for this work on the OC and responded that,

At the City Creek site, I found some fault strands not too far north of the Highland Avenue bridge…There may also have been other strands farther north, but that part of the trench traversed through boulder gravel, so it was difficult or impossible to identify whether or not there were any faults there.

Figure 3 from Professor McGill shows the location of her trench and includes her observation that,

I was not convinced that the faults that I did see in the southeastern half of the part that I re-opened necessarily represented the main strand of the fault.



3. As can be seen in Figure 2, transversely oriented trenches were excavated where potential faults parallel to the main trace and crossing beneath the OC would have likely have been encountered. However the observation of faults southeast of the mapped trace and northeast of the OC, as well as LOTBs for both the OC and City Creek Bridge (Br. #54C-0600) revealing materials permissive of faulting (e.g, clayey coarse sand with rock fragments may have resulted from shearing) suggest that there may be minor faults located northeast and perhaps crossing beneath the OC. It is very unlikely that the main trace crosses beneath the OC.

Review of aerial photos/Lidar data Non-stereo aerial photos taken in 1994 and 1996 were reviewed. Man-made features such as the OC, highway, and urban development limited the usefulness of the photos. The trench shown in Figure 4 was identified in the 1996 photo. Lidar imaging was not useful again because of development and ground modification in the area. Field Reconnaissance A field reconnaissance was conducted on 11/30/2012, by K. Douglas Cook, CEG from the Office of Geotechnical Design South II and Martha Merriam. Road construction, vegetation, and natural erosion have concealed or removed any evidence of faulting in this area. We identified several areas where trenching would be feasible (i.e., directly northwest of the OC and northeast of the OC near the northbound onramp from Highland Avenue) if field exploration at the site is required. POTENTIAL FOR FAULT RUPTURE It is likely that the main trace of the San Andreas Fault (San Bernardino South Branch) is located as mapped on Figures 1-3. McGill’s observation of minor faulting nearer the OC and the LOTBs revealing materials permissive of faulting indicate that minor faults (that may or may not be active) may be nearer or beneath the OC. It is also prudent to assume there may be errors in the locations, etc., since the fault was not observed in the field. Fault parameters used include M7.9 as the estimated maximum magnitude earthquake expected for the San Bernardino South Branch of the San Andreas Fault. Estimated slip rate for this section is 13 mm/yr, based on measurements obtained at the Plunge Creek paleosite 3 miles SE of the Highland Avenue OC (Dawson and Weldon, 2012). An aseismic slip factor of 0 was used (Bryant et al, 2002). The main trace (approximately located) is 100 m northeast of the OC and was weighted 90%, and a secondary trace (inferred) assumed to cross beneath the OC was weighted 10%. Since the fault is well studied at this latitude, a probabilistic approach was used to estimate displacement. Per



methods described in the introduction the expected offset at the OC on a fault oriented parallel to the San Andreas Fault (San Bernardino South Branch) but located anywhere beneath the OC was estimated to be 3/4 m or 2-1/2 feet (Figure 4). RECOMMENDATIONS FOR ADDITIONAL INVESTIGATIONS No additional work is recommended at this time. Only secondary (inactive or low activity?) traces potentially cross beneath the OC. If the OC cannot withstand the design displacement, further work such as trenching/geophysical studies to locate the secondary traces and evaluate their activity can be performed.

If you have any questions, please contact Martha Merriam at (916) 227-7135.

Prepared by: Date: February 13, 2013

Martha Merriam, C.E.G.

Engineering Geologist Office of Geotechnical Support Instrumentation Branch

cc: Geotechnical Support Shira Rajendra Geotechnical Design – South 2 Abbas Abghari

GS (Instrumentation Branch) Gem-Yeu Ma Research and Innovation Tom Shantz Office of Earthquake Engineering Fadel Alameddine



REFERENCES Abrahamson, N., 2008, Appendix C, Probabilistic Fault Rupture Hazard Analysis, San Francisco PUC, General Seismic Requirements for the Design on New Facilities and Upgrade of Existing Facilities. Bryant, W.A., and Lundberg, M.Matthew, compilers, 2002, Fault number 1i, San Andreas fault zone, San Bernardino Mountains section, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, http://earthquakes.usgs.gov/hazards/qfaults, accessed 02/05/2013 10:25 AM. CGS, 2002, Guidelines for evaluating hazard of surface fault rupture, CGS Note 49: http://www.conservation.ca.gov/cgs/information/publications/cgs_notes/note_49/Documents/note_49.pdf Caltrans, 2012 (draft), MTD 20-10, Fault Rupture: http://onramp.dot.ca.gov/hq/esc/sd/bridge_design/gec/documents/MTD20-10%209%2024%2012.pdf

Caltrans, 1996, 9x18 air photos dated 1994, 1:2400

Caltrans, 1994, 9x18 air photos dated 1994, 1:2400

Caltrans, 1992, As-Built Log of Test Borings (exploration during April,1989), Highland Avenue OC #54-1086.

Caltrans, 1992, As-Built Log of Test Borings (exploration during April/May, 1989), City Creek Bridge #54C-0600. Leighton and Assoc., 1997, Supplemental geologic investigation of faulting, assessors parcel No. 1199-311-05, Highland Avenue and Highway 330, City of San Bernardino, California, November 20, 1997 (AP Report 3098). Leighton and Assoc., 1977, Geotechnical investigation, tentative tract 9916, City of San Bernardino, CA, July 22, 1977 (AP Report 651). McGill, S., and others, 1998, Prehistoric earthquakes on the San Andreas Fault, San Bernardino, California: EOS 79, 301. Petersen, M., and others, 2011, Fault displacement hazard for strike-slip faults: Bulletin of the Seismological Society of America, Vol. 101, No. 2, pp. 805–825.



Rasmussen, G.S., and Assoc., 1998, Subsurface engineering geology investigation, Cultural and Retail Center, Highland and Boulder Avenues, Highland, California, June 3, 1998 (AP Report 3112).

US Geological Survey, 2011, http://earthquake.usgs.gov/hazards/qfaults/google.php

Wells, D., and Coppersmith, K., 1994, New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement: Bulletin of the Seismological Society of America, Vol. 84, No. 4, pp. 974-1002. Williams, F.J., 1997, review of Leighton and Assoc. report dated November 20, 1997 (see full reference above) (Part of AP Report 3098). Wong, P., Bryant, W.A., and Treiman, J.A., 2003, Fault investigation reports for development sites within A-P EFZ zones in Southern California, 1974-2000: CD2003-002.

Figure 1. Area fault map (USGS 2011; Wong et al, 2003).

Legend: Black lines – EFZ. Orange lines – main trace of San Andreas Fault (San Bernardino South Branch). Yellow lines – older traces of San Andreas Fault (Mill Creek section). Orange polygons – AP study areas.



/ Figure 2. Locations of nearby trenches and dates excavated are shown in red. Main trace of San Andreas Fault (San Bernardino South Branch) is shown in orange (Holocene-latest Pleistocene) from USGS (2011). 1990 trench not referred to in text did not encounter any faults (K.Doug Cook, p.c., 2012).



Figure 3. Preliminary map obtained from Sally McGill, CSU San Bernardino, p.c., 2013. Annotations by McGill.



Figure 4. Probabilistic offset at Highland Ave OC, assuming 90% displacement on main fault trace and 10% on a minor fault trending beneath the OC is 0.75 m (2-1/2 feet) in both cases.