1. Rotation Workshop 2/16/20061 Observational Experience with Rotational Strong Motion Robert Nigbor UCLA

2. Rotation Workshop 2/16/20062 Outline  Motivation  Early 1993 6DOF deployment  9/93 NPE blast measurement  BVDA deployment, 12/93 – present  GVDA SFSI Test Structure 6DOF measurements, 2004-present  Thoughts on future sensor selection

3. Rotation Workshop 2/16/20063 Motivations for 6DOF Deployment 1.Scientific interest per Bouchon & Aki 1982 “Strain, tilt, and rotation associated with strong ground motion in the vicinity of earthquake faults”, BSSA 72 2.Sensitivity of conventional strong motion accelerometers to rotational motions

4. Rotation Workshop 2/16/20064 Sensitivity of Linear Accelerometers to Rotational Motions: from IEEE Standard Specification Format Guide and Test Procedure for Linear, Single-Axis, Nongyroscopic Accelerometers Rotation terms

5. Rotation Workshop 2/16/20065 Rotation terms

6. Rotation Workshop 2/16/20066 Rotational Sensor Selection in 1993  Unfunded “Skunkworks” project, so budget was small  Looked at FOG, RLG’s but cost was too high (and power/reliability was a question)  Systron-Donner QRS11 “Gyrochip” was brand new in 1993, manufacturer was eager to help with potential new applications, gave discount price of $3k for three.  Range (0.2 rad/sec clip, 1e-4 rad/sec stated resolution) seemed right per Bouchon & Aki and other analytical estimations of rotational velocities for strong ground motion

7. Rotation Workshop 2/16/20067 6DOF Prototype System

8. Rotation Workshop 2/16/20068 Sensor Package (with FBA-23) 3-component rotation sensor 3-component accelerometer (FBA-23)

9. Rotation Workshop 2/16/20069 Aftershock Monitoring  Installed in my garage for a month, no earthquakes (but could observe rotational data during jumping & hammering near the sensor)  Installed in a private home garage north of Landers, 2km from the Landers EQ fault trace, for 2 months. Six small aftershocks recorded, maximum PGA was 0.015g. No rotational motion was resolved above the ~.001rad/sec channel noise level.

10. Rotation Workshop 2/16/200610 NPE “Chemical Kiloton” Event “The DOE conducts a Non-Proliferation Experiment at the Nevada Test Site The U.S. Department of Energy (DOE) detonated approximately 1.29 million kg of a commercial blasting agent, based on ammonium nitrate and fuel oil (ANFO), at the Nevada Test Site (NTS) on September 22, 1993, at 00:01.080 AM Pacific Daylight Time. The blasting agent was emplaced in a cylindrical chamber, approximately 15.2 m in diameter by 5.5 m high, located at 37.20193 N and 116.20986 E in a Rainier Mesa tunnel, 390 m underground. Code-named the Non-Proliferation Experiment (NPE), the explosion had an energy release of approximately 1 kt (1 kiloton = 4.186x1012 joules).” J. Zucca, EOS, Nov. 1993

11. Rotation Workshop 2/16/200611 6DOF Accelerograph Installation for the NPE  Opportunity for a piggyback experiment, encouraged and facilitated by Fred Followill & Jay Zucca  1km from ground zero (blast was 390m underground)  Sensors bolted on a small partially-embedded concrete pedestal at the bedrock site on top of Rainer Mesa  Unattended triggered recording  No photos…

12. Rotation Workshop 2/16/200612 NPE Results

13. Rotation Workshop 2/16/200613 NPE Waveforms

14. Rotation Workshop 2/16/200614 1-sec Subset

15. Rotation Workshop 2/16/200615 Displacements

16. Rotation Workshop 2/16/200616 Installation at Borrego Valley Downhole Array (BVDA)  Installed along with FBA-23 at ground level at center of BVDA in Dec. 1993  Still in place (array is now operated by UCSB & Jamie Steidl)  Free-field site on 220m of stiff sand over granite  Less than 2km from Coyote Canyon Fault at the south end of the Anza seismic slip gap  Hundreds of earthquakes recorded, maximum PGA ~0.2g, no resolvable rotational motions above 0.001 rad/sec yet! Peak velocity contours from 3D FD simulation of M4.9 event; from Olsen, K., Nigbor, R., and T. Konno, “3-D Viscoelastic Wave Propagation in the Borrego Valley, California, Constrained by Borehole and Surface Data,” BSSA 90, 1, 2000

17. Rotation Workshop 2/16/200617 SFSI Test Structure at Garner Valley Digital Array (GVDA) 3D rotational velocity sensor in center of bottom slab

18. Rotation Workshop 2/16/200618 DAQ is a 24-bit Digitexx System

19. Rotation Workshop 2/16/200619 Small Local Earthquake Rotation:(Ch.8–Ch.10)/374cm peak base acceleration (cm/s 2) = 1.3(NS), 2.0(EW), 0.9(V)

20. Rotation Workshop 2/16/200620 Small Local Earthquake Vertical Bottom Slab Corner Accelerations & Difference

21. Rotation Workshop 2/16/200621 Forced Vibration - Internet Controlled Shaker Time (s) Acceleration (cm/s 2 ) 060 5 -5

22. Rotation Workshop 2/16/200622 GVDA/SFSI Forced Vibration Derived Rotation: Ch. 8 - 10

23. Rotation Workshop 2/16/200623 SFSI Forced Vibration Rotational Velocity:Derived from Av & Measured by ATA ARS-09 Gyro

24. Rotation Workshop 2/16/200624 Conclusion Regarding Experience with ATA Gyro at GVDA  Dynamic range of ATA ARS-09 gyro is ~60dB, less than the 100dB in the spec  Resolution is about 5E-3 rad/sec broadband, maybe 1E-3 rad/sec narrowband  Small rotational foundation motion can be resolved using closely-spaced vertical accelerometers if done carefully and with high resolution sensors/digitizers. Ground motion will be tougher, as rotation is proportionally much smaller. and available  The nees@UCSB SFSI Test Structure at GVDA is a useful (and available) field test facility for rotational sensors.

25. Rotation Workshop 2/16/200625 Future RotationSensor Selection  Cost, reliability, and power consumption are key parameters for 6DOF strong motion systems – the fancy stuff (FOG, RLG) may not be appropriate for most applications.  Linear acceleration cross-axis sensitivity may be critical for our application, and should be experimentally characterized for selected sensors (ARS-09 spec is <0.009 rad/sec per g).  No need to reinvent this wheel  No need to reinvent this wheel: The IEEE Aerospace and Electronic Systems Society (AESS) has worked through most of the instrumentation issues for gyroscopic sensors Industry standards and guidelines are available for our use, as they are for accelerometers

26. Rotation Workshop 2/16/200626 IEEE Standards for Gyros