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Status of ENA Database of Ground Motions for NGA East
A Presentation by Chris CramerAt the NGA East Workshop on
Database DevelopmentSeptember 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 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 (?)
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
SCR Observations for M>6?
• 2001 M7.6 Bhuj Earthquake?
• 1988 M5.8-6.0 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
MNT
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
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