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

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

Overview Current Status Issues

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

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

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

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)

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)

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

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

Initial List of Additional Events M 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 (?)

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

SCR Observations for M>6? 2001 M7.6 Bhuj Earthquake? 1988 M Saguenay Earthquake? – Selected, more “normal” records Others?

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

Ebel, 2002 MNT

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

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

Rock Only | Mix of Soil and Rock

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