Status of ENA Database of Ground Motions for NGA East

1. Status of ENA Database of Ground Motions for NGA East A Presentation by Chris Cramer At the NGA East Workshop on Database Development September 29, 2009

2. Summary • Collected Waveforms from ENA M>4 since 2000 • Initial Processing Procedure Developed • Remaining Issues • Magnitude Assignment • Data from Distances < 100 km • SRC Events with M>6 • Identify Source Effects • Lack of Vs30 Measurements

3. Overview • Current Status • Issues

4. Current Status • Funding • Event Selection • Waveform Sources • Summary of Processing • Quality Assurance

5. Funding and Initial Data Selection • The NRC has Provided the Initial Funding for the Database Development for ENA, now completed • Initial Focus was on available M>4 ENA Earthquakes since January 1, 2000 • Selected and Collected Data for 28 Events, including 2008 Mt. Carmel mainshock and 3 aftershocks - see handout Table 1

8. Waveform Sources • IRIS – ANSS and LDCN, mainly • CNDC • Others • CERI • SLU • VT • NESN

9. Summary of Processing • Data Processing using Seismic Analysis Code (SAC) • Download Uncorrected Waveforms and PZ Files • Review Waveforms for Obvious Problems • Instrument Correction and Initial Filtering • Generate Signal and Pre-event Noise Spectra and Select Final Filter Corners • Final Bandpass Filtering for Acc, Vel, Dsp • Extract NGA Ground Motion Values (PGA, PGV, PGD, and 105 Sa)

10. Instrument Correction and Filtering • Instrument Correction • Remove Mean and Detrend(linear) • SAC TRANSFER Function • PZ Files (for Displacement) • Successively Specify Acc, Vel, none (Dsp) • Waveform Filtering • Frequency Domain, Acausal, Cosine-Tapered Bandpass Filter in SAC TRANSFER Function • Checked via Dave Boore’s Processing and Butterworth Filtering (same results)

12. Quality Assurance • Examine Original Waveforms • Clipping/Distortion • Missing Data / Noise Spikes, etc. • Determine Spectral Signal to Noise • Final Filter Selection • Plot PGA (PGV) vs. Distance • PZ or Instrument Problems (outliers) • Build Waveform Quality Table for each Event

14. Issues • Lack of Observations less than 100 km • Event Magnitudes (Location) • SCR Observations for M>6? • Radiation/Source Effects • Limited Station Vs Information (Vs30)

15. Initial List of Additional EventsM 2.5 to 4 w/ 5 Stn < 100 km • Table 5 of Handout • 4 New Madrid SZ events • 3 Charleston SZ events • 4 Charlevoix SZ events • 4 Ottawa Area events • 2 Lake Ontario events • Added Goal of Regional Balance (?)

16. Importance of Event Magnitude • Table 2 of handout • MW estimates vary by 0.2 – 0.4 • Factor of Two in Amplitude • Examples of Impact – Mt Carmel Earthquake • PGA • 1.0 s Sa

21. SCR Observations for M>6? • 2001 M7.6 Bhuj Earthquake? • 1988 M5.8-6.0 Saguenay Earthquake? • Selected, more “normal” records • Others?

23. Radiation/Source Effects • 2002 Au Sable Forks Earthquake • Focal Mechanism • Ground Motion vs. Distance Plot • PGA • 1.0 s Sa

24. MNT Ebel, 2002

25. MNT

26. MNT

27. Vs30 Availability • Limited Existing Information • See Table 4 of handout • Need for making Vs measurements at important sites

29. Importance of Site Condition • Ground Motion Data Scatter Increases When Soil Sites are Added to Hard Rock Observations. • Example from Riviere du Loup Earthquake • PGA • 1.0 s

30. Rock Only | Mix of Soil and Rock

31. Rock Only | Mix of Soil and Rock

32. Summary • Collected Waveforms from ENA M>4 since 2000 • Discussion of additional events this afternoon • Initial Processing Procedure Developed • Further Discussion this afternoon • At Least Five Remaining Issues • Discussion this afternoon