HR: 0830h
AN: S21D-0319    [PDF]
TI: The Rupture Characteristic of 1999 Izmit Sequence Using IRIS Data
AU: * Konca, A O
EM: ozgun@gps.caltech.edu
AF: Seismological Laboratory, California Institute of Technology, Seismo Lab, 252-21 Pasadena CA 91125, Pasadena, CA 91125 United States
AU: Helmberger, D V
EM: helm@gps.caltech.edu
AF: Seismological Laboratory, California Institute of Technology, Seismo Lab, 252-21 Pasadena CA 91125, Pasadena, CA 91125 United States
AU: Ji, C
EM: jichen@gps.caltech.edu
AF: Seismological Laboratory, California Institute of Technology, Seismo Lab, 252-21 Pasadena CA 91125, Pasadena, CA 91125 United States
AU: Tan, Y
EM: ytan@gps.caltech.edu
AF: Seismological Laboratory, California Institute of Technology, Seismo Lab, 252-21 Pasadena CA 91125, Pasadena, CA 91125 United States
AB: The standard source studies use teleseismic data ($30\deg$ to $90\deg$) to analyze earthquakes. Therefore, only a limited portion of the focal sphere is involved in source determinations. Furthermore, the locations and origin times of events remain incompatible with local determinations. Here, we attempt to resolve such issues by using IRIS data at all distances, leading to more accurate and detailed rupture properties and accurate relative locations. The 1999 Izmit earthquake sequence is chosen to test our method. The challenge of using data outside the conventional teleseismic distance range is that the arrival times and waveforms are affected more by the Earth structure. We overcome this difficulty by calibrating the path effects for the mainshock using the simpler aftershocks. Therefore, it is crucial to determine the source parameters of the aftershock. We constructed a Green's function library from a regionalized 1-D model and performed a grid search to establish the depth and fault parameters based on waveform matching for the Pnl waves between the synthetics and data, allowing the synthetics in each station to shift separately to account for the path effect. Our results show that the earthquake depth was around 7 km, rather than 19 km from local observatory (Kandilli) and 15 km from the Harvard's CMT solution. The best focal mechanism has a strike of $263\deg$, a dip of $65\deg$, and a rake of $180\deg$, which is very close to the Harvard's CMT solution. The waveform fits of this aftershock is then used as a criterion to select useful source-station paths. A path with a cross-correlation value above 90% between data and synthetics is defined as a "good path" and can be used for studying the Izmit and Duzce earthquakes. We find that the stations in Central Europe and some of the Greek Islands are "good paths", while the stations in Northeast Africa and Italy cannot be used. The time shifts that give the best cross-correlation values are used to calibrate the picks of the Izmit and Duzce events. We realize that this is a very objective way to pick arrival times. However, our preliminary inversions using teleseismic data for Duzce and Izmit events show that handpicked P and S arrival times of the same station from two very close events are not always well correlated. Obviously, how we pick the arrival time governs the rupture pattern and rupture velocity. Therefore, our methodology brings a more objective approach to pick the travel times. To the end, we will invert for the source history of the Duzce and Izmit earthquakes with the regional data and compare with the inversion result using teleseismic data. Moreover, predictions of the teleseismic data, using the solution from the inversion using regional phases will be presented.
DE: 7200 SEISMOLOGY
SC: Seismology [S]
MN: 2003 Fall Meeting