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Stress Drop Estimates Using the Attenuation Parameter Kappa for Earthquakes in the SCEC/USGS Community Ridgecrest Dataset

Description: 

Estimates of earthquake stress release, regional attenuation and site effects are needed for ground motion prediction and are essential to improve our understanding of the factors controlling both the statics and dynamics of the rupture process. The ongoing community stress drop validation study is aimed at improving measurements of these fundamental parameters. Calderoni et al. (2010, 2014) developed a two-step approach to modeling attenuation and then estimating source parameters from individual earthquake spectra. To test and verify this spectral fitting approach we apply it to the common dataset provided by the community study. The dataset consists of 2 weeks of earthquakes in the 2019 Ridgecrest, California, sequence.

Following Calderoni et al., 2019 first we calculate the regional kappa attenuation (k) parameter by averaging 6 earthquakes with magnitude from 5.0 to 5.6. We select these large, well recorded events to estimate spectral falloff because they have the best signal-to-noise ratio over the widest frequency range. We correct the spectra using the k parameter and normalize to unit distance. Second, we estimate the site term accounting for attenuation and amplification in the near‐surface beneath the station. For each event, we average the attenuation-corrected scaled spectra at available stations and compute the difference from the mean event spectrum for each station. These differences are averaged over the event ensemble to obtain a mean site term for each station. We then correct each recorded velocity spectrum for regional attenuation using the k values and for the site effects calculated at each station. We then fit the resulting source spectra assuming a simple circular source model (e.g., Brune, 1970; Madariaga, 1976) to estimate the corner frequencies and stress drop of each event. We investigate how selection choices used in the analysis including station selection and signal frequency range affect the results and compare our measurements with those of other research groups.

Session: Understanding the Variability in Earthquake Stress Drop Measurements [Poster]

Type: Poster

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Giovanna Calderoni

Student Presenter: No

Invited Presentation: 

Authors