Source Parameters of Regional Earthquakes in Taiwan : January-December , 1998

We report source parameters of 49 earthquakes that occurred between January and December, 1998, in the Taiwan region. The improved CMT inversion algorithm by Kao et al. (1998) is used to overcome the generally higher background noise as well as the heterogeneous velocity structure resulted from the complex tectonic interactions near Taiwan. To make the results more accessible and useful to the academic community, both the table that summarizes the reported source parameters and the complete set of inversion results are available electronically from the BA TS world­ wide web site at http://bats.earth.sinica.edu.tw/CMT_Solutions/cmtF1998.html. (

Successful development of the centroid-moment-tensor (CMT) inversion technique in the early 1980's has enabled the systematic determination of source parameters for global large and moderately-sized earthquakes (e.g., Dziewonski et al. 1981;Kawakatsu et al. 1995;Sipkin 1982).The CMT inversion technique was later successfully applied to regional earthquakes because of the increasing knowledge of detailed velocity structures on a regional scale and the establishment of regional broadband networks (e.g., Dreger and Helmberger 1993;Fan and Wallace 1995;Lay et al. 1994;Thio and Kanamori 1995;Zhao and Helmberger 1994).Consequently, the routine CMT solution reports for smaller, regional earthquakes has become standard practice for many regional broadband seismographic networks (e.g., Zhu and Helmberger 1996;Pasysnos et al. 1996).
Establishment of the "Broadband Array in Taiwan for Seismology (BATS)" has enabled the systematic determination of reliable source parameters for regional earthquakes in Taiwan through the CMT technique (Kao et al. 1998).The network began its test operation in late 1994 (Fig. 1).A brief description of the BATS configuration and operation can be found in Kao et al. (1998Kao et al. ( , 2001) ) and Kao andJian (1999, 2001).The Data Management Center of the Fig. 1.Map of the "Broadband Array in Taiwan for Seismology (BATS)".Solid and gray squares show stations currently in operation and under construction, respectively.In addition to the permanent stations, BATS includes 17 portable stations that can be deployed for specific research tasks.
Institute of Earth Sciences (DMC-IES), Academia Sinica is responsible for BATS data archiving and distribution.One copy of BATS data is contributed to the Data Management Center of the Incorporated Research Institutions for Seismology (DMC, IRIS) for the same purpose.Interested readers can obtain updated information at BATS worldwide web site (http://bats.earth.sinica.edu.tw).
Our CMT algorithm begins with a background-noise evaluation that determines the frequency band used in the inversion.The cut-off frequency of the lower corner is usually at ~0.02 Hz, which is determined by comparing the power spectra of waveform windows 300 s before and after the P first arrival (Kao et al. 1998).We also utilize a two-step procedure to allow different velocity models for different station-source pairs.This is to mimic the effect of heterogeneous velocity structures in the Taiwan region.For more technical details, readers are referred to our previous reports (Kao et al.1998;Kao and Jian 1999).
To characterize the inversion quality, each inversion result is classified using a letter (A-F) and a digit (1-4) combination depending on two parameters: the waveform misfit (E) and the CLVD component amount (ε ), respectively.The derivations of E and ε were presented in our previous reports (Kao et al. 1998;Kao and Jian 1999) and listed in Table 1.
Table 1.Quality classification of the inversion results.
Following the criteria defined in Kao and Jian (1999), we report on source parameters only if they meet the following criteria: (1) 3-component waveforms from at least three stations are used in the inversion, and (2) the inversion quality must be higher than C4.A total of 194 earthquakes that satisfy these conditions are listed in Table 2.The epicenters for all of these studied earthquakes are plotted in Figs.2a, b and the corresponding moment-tensor solutions and focal depths are plotted in Fig. 2c.Due to practical concerns, the inversion results are presented as an electronic appendix to this report.Interested readers can download the complete set from the BATS worldwide web site at http://bats.earth.sinica.edu.tw/CMT_Solutions/cmtF2002.html.To make the results more accessible and useful to the academic community, Table 2 and the tables in our previous reports showing the source parameters of earthquakes between 1995 and 2001 (Kao and Jian 1999;Kao et al. 2001Kao et al. , 2002aKao et al. , 2002b;;Liang et al. 2003) are also available from our web site (http://bats.earth.sinica.edu.tw/CMT_Solutions/).

Fig. 2a .
Fig. 2a.Moment-tensor inversion results.(a) Map showing the epicenters of 194 studied earthquakes.The size and shade of each symbol represent the corresponding moment magnitude and focal depth, respectively, as shown by the scales.Event numbers are according to Table 2.