Classification of Main Shocks and Aftershocks in the NGA-West2 Database

Abstract

Previous studies have found a systematic difference between short-period ground motions from aftershocks and main shocks, but have not used a consistent methodology for classifying earthquakes in strong motion data sets. A method for unambiguously classifying earthquakes in strong motion data sets is developed. The classification is based on the Gardner and Knopoff time window, but with a distance window based on a new distance metric, CRJB, defined as the shortest horizontal distance between the centroid of the surface projection of the potential aftershock rupture plane and the surface projection of the main shock rupture plane. Class 2 earthquakes are earthquakes that have a CRJB distance less than a selected limit and within a time window appropriate for aftershocks. All other earthquakes are classified as Class 1. For maximum CRJB of 0 km and 40 km, 11% and 36% of the earthquakes in the NGA-West2 database are Class 2 events, respectively.

NGA-West2 Equations for Predicting Vertical-Component PGA, PGV, and 5%-Damped PSA from Shallow Crustal Earthquakes

“…We consider ground motions from Class 1 (CL1: mainshocks) and Class 2 (CL2: aftershocks) events, using the minimum centroid JB R separation of 10 km from Wooddell and Abrahamson (2014) based on subjective interpretation of results from exploratory analysis. Records are screened to include only those periods within the usable frequency band for the vertical-component, and to exclude any records flagged as questionable by manual inspection (as described by Ancheta et al, 2014;specifically, we require that the "Spectra Quality Flag" under Column JK in the flatfile equals 0).…”

Strong Ground Motion Characteristics from 2016 Central Italy Earthquake Sequence

“…in the NGA-West2 project (Bozorgnia et al, 2014) that considers the Gardner-Knopoff time window in combination with between-event distance metric CRJB, defined as the distance from the centroid of the surface projection of the possible aftershock rupture surface to the surface projection of the mainshock rupture plane (Wooddell and Abrahamson, 2014). Both approaches provide similar results for the subject events.…”

Building service life economic loss assessment under sequential seismic events

“…Each pair consists of an as‐recorded mainshock‐aftershock ground motion sequence. The classification of the second ground motions in the record‐pairs as aftershocks is done using the time and distance windowing algorithms developed by Knopoff and Gardner and Wooddell and Abrahamson . The ground motion pairs are from the Class 1 (mainshock) and Class 2 (aftershock) records of the Northridge, Livermore, Coalinga, Landers, Mammoth Lakes 01, Whittier Narrows, Darfield and Chi‐Chi earthquakes, which are available in the PEER‐NGA West2 database .…”

“…The ground motion pairs are from the Class 1 (mainshock) and Class 2 (aftershock) records of the Northridge, Livermore, Coalinga, Landers, Mammoth Lakes 01, Whittier Narrows, Darfield and Chi‐Chi earthquakes, which are available in the PEER‐NGA West2 database . A magnitude‐dependent time window and a distance threshold of 40 km measured in terms of the centroidal Joyner‐Boore distance is used to identify the aftershock ground motions following a mainshock event. The magnitudes of the events that produced the selected ground motions range from 5.8 and 7.6 for mainshocks and 5.2 and 6.5 for aftershocks.…”

“…The classification of the second ground motions in the record-pairs as aftershocks is done using the time and distance windowing algorithms developed by Knopoff and Gardner 26 and Wooddell and Abrahamson. 27 The ground motion pairs are from the Class 1 (mainshock) and Class 2 (aftershock) records of the Northridge, Livermore, Coalinga, Landers, Mammoth Lakes 01, Whittier Narrows, Darfield and Chi-Chi earthquakes, which are available in the PEER-NGA West2 database. 28 A magnitude-dependent time window and a distance threshold of 40 km measured in terms of the centroidal Joyner-Boore distance 27 is used to identify the aftershock ground motions following a mainshock event.…”