Figure 1: A) Map of Kocaeli Earthquake aftershock zone. The black concentric circles centered on the mainshock epicenter are in 20-km increments. The red circles are aftershock locations (from Seismological Observatory, KOERI: Seismology, Recent Earthquakes Text) and their radii are proportional to Brune-source radii, the magnitudes of the four largest events are annotated. The blue diamonds are the locations of individual seismographs and/or small-aperture seismic arrays, and they are connected by dotted lines to the town names of the recording sites. B) The corresponding three-components (Z, N, E) of ground motion recorded at these sites are shown as a pseudo-recordsection of 40-s duration. The amplitudes of each trace are normalized to the peak value of that trace, i.e., amplitudes cannot be compared. Strong-motion records are plotted as acceleration in the eastern epicentral region, weak-motion records are plotted as velocity in Avcilar and West Istanbul.