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