Augmented Relocated Earthquake Catalog and Phase-Arrivals from data recorded on the Karadere-Duzce branch of the North Anatolian Fault during the 1999 Izmit-Düzce Earthquake Sequence

This dataset provides relocated and augmented earthquake catalogs for the 1999 İzmit–Düzce earthquake sequence along the Karadere–Düzce branch of the North Anatolian Fault in northwestern Türkiye. The original earthquake and waveform data were derived from the seismic dataset analyzed by Peng and Ben-Zion (2006). Differential arrival times were measured through waveform cross-correlation. These differential-time measurements were subsequently used in a double-difference relocation procedure to refine relative origin times and hypocentral locations. Local magnitudes (ML) were recalculated from instrument-response-corrected continuous waveforms. Horizontal-component waveforms were transformed into simulated Wood–Anderson displacement seismograms, and the resulting displacement amplitudes were used to calculate station and event local magnitudes. The dataset contains two catalogs: The primary relocated catalog contains 13,435 earthquakes from 25 August 1999 to 10 February 2000 and 98,509 event–station phase records. These events were derived from the catalog and waveform data reported by Peng and Ben-Zion (2006). The augmented relocated catalog contains 16,440 detected events from 25 August 1999 to 13 February 2000 and 86,858 event–station phase records. Detection and location were performed using only the temporary YJ network. Because of its sparse and uneven station coverage, the augmented hypocentral locations may have large uncertainties. This catalog is therefore intended primarily as an event-detection record and should not be treated as a uniformly well-constrained relocated catalog. Both catalogs use metadata for 33 seismic stations. File organization Relocated.ctlg: Primary waveform-cross-correlation-based relocated catalog. Each row contains UTC origin time, latitude and longitude in decimal degrees, depth in kilometres, and Wood–Anderson-based local magnitude (ML). Relocated.pha: Phase file corresponding to Relocated.ctlg. Event headers contain UTC origin time, latitude, longitude, depth, and local magnitude. Station records contain the network/station code, P- and S-wave arrival times, and Wood–Anderson displacement amplitude in metres. Augmented_Relocated.ctlg: Augmented detection-based relocated catalog. Each row contains UTC origin time, latitude, longitude, depth, local magnitude, and a location-quality flag. Augmented_Relocated.pha: Phase file corresponding to Augmented_Relocated.ctlg. Event headers are followed by network/station codes, P- and S-wave arrival times, and displacement amplitudes in metres. station_info.txt: Station metadata, including station code, latitude and longitude in decimal degrees, and elevation in metres. Location-quality flags The final column of Augmented_Relocated.ctlg provides a relative location-quality classification based on the formal horizontal and vertical errors reported by HypoDD: good: horizontal formal error ≤ 200 m and vertical formal error ≤ 200 m. normal: not classified as good, but horizontal formal error ≤ 500 m and vertical formal error ≤ 1000 m. bad: horizontal formal error > 500 m or vertical formal error > 1000 m. Because the relocation used the LSQR solver, these formal errors should be treated as relative quality indicators rather than rigorous hypocentral confidence intervals. Accompanying figures The data-continuity figure summarizes the temporal availability of continuous waveform data at individual YJ stations. The travel-time diagnostic figure shows the relationship between S–P time and hypocentral distance, together with the P- and S-wave travel-time curves. It provides an overview of the phase-pick distribution and its consistency with source–station distance. This dataset is a derived data product. Users should cite both this Zenodo dataset and the original study by Peng and Ben-Zion (2006).