A New Method for Determining Small Earthquake Source Parameters Using Short-Period P Waves

نویسندگان

  • Ying Tan
  • Don Helmberger
چکیده

We developed a new technique of inverting short-period (0.5–2 Hz) P waveforms for determining small earthquake (M 3.5) focal mechanisms and moments, where magnitude 4 events with known source mechanisms are used to calibrate the “unmodeled” structural effect. The calibration is based on a waveform cluster analysis, where we show that clustered events of different sizes, for example, M 4 versus M 2, display similar signals in the short-period (SP, 0.5–2 Hz) frequency band, implying propagational stability. Since both M 4 and M 2 events have corner frequencies higher than 2 Hz, they can be treated as point sources, and the “unmodeled” structural effect on the SP P waves can be derived from the magnitude 4 events with known source mechanisms. Similarly, well-determined magnitude 2’s can provide calibration for studying even smaller events at higher frequencies, for example, 2–8 Hz. In particular, we find that the “unmodeled” structural effect on SP P waves is mainly an amplitude discrepancy between data and 1D synthetics. The simple function of “amplitude amplification factor” (AAF) defined as the amplitude ratio between data and synthetics provides useful calibration, in that the AAFs derived from different clustered events appear consistent, hence stable and mechanism independent. We take a grid-search approach to determine source mechanisms by minimizing the misfit error between corrected data and synthetics of SP P waves. The validation tests with calibration events demonstrate the importance and usefulness of the AAF corrections in recovering reliable results. We introduce the method with the 2003 Big Bear sequence. However, it applies equally well to other source regions in southern California, because we have shown that the mechanism independence and stability of the AAFs for source regions of 10 km by 10 km are typical. By definition, the AAFs contain the effects from the station site, the path, and crustal scattering. Although isolating their contributions proves difficult, the mechanism independence and stability of the AAFs suggest that they are mainly controlled by the near-receiver structure. Moreover, the ratios between the AAFs for the vertical and radial components from various events at different locations appear consistent, suggesting that these AAF(v)/AAF(r) ratios might be simple functions of site conditions. In this study, we obtained the focal mechanisms and moments for 92 Big Bear events with ML down to 2.0. The focal planes correlate well with the seismicity patterns, while containing abundant finer-scale fault complexity. We find a linear relationship between log(M0) and ML, that is, log(M0) 1.12ML 17.29, which explains all the data points spanning three orders of magnitude (2.0 ML 5.5).

برای دانلود رایگان متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

\ k RESEARCH IN SEISMOLOGf PROGRESS REPORT IN EARTHQUAKE MECHANISM . MAGNITUDE , SPECTRAL PROPERTIES . AND MODEL STUDIES

The research may be categorized as work on: earthquake focal mechanisms, earthquake and explosion magnitude and energy determinations, spectral properties of earthquakes and explosions, model studies of strain release and coupling and continued study of regional seismicity. The principal results reported are: (l) an improved technique for determining the best-fitting focal mechanism relation by...

متن کامل

Single station estimation of earthquake early warning parameters by using amplitude envelope curve

In this study, new empirical relationships to estimate key parameters in Earthquake Early Warning (EEW) system including magnitude, epicentral distance and Peak Ground Acceleration (PGA) are introduced based on features of the initial portion of P-wave’s amplitude envelope curve. For this purpose, 226 time series recorded by bore-hole accelerometers of Japanese KiK-net are processed for earthq...

متن کامل

Source Mechanism and Rupture Directivity of the 18 May 2009 M W 4 . 6 Inglewood , California , Earthquake

On 18 May 2009, an Mw 4.6 earthquake occurred beneath Inglewood, California, and was widely felt. Though source mechanism and its location suggest that the Newport–Inglewood fault (NIF) may be involved in generating the earthquake, rupture directivity must be modeled to establish the connection between the fault and the earthquake. We first invert for the event’s source mechanism and depth with...

متن کامل

Short Note Earthquake Centroid Locations Using Calibration from Ambient Seismic Noise

Earthquakes occur in complex geology, making it difficult to determine their source parameters and locations because of uncertainty in path effects. We can avoid some of these problems by applying the cut-and-paste (CAP) method, which allows for timing shifts between phases, assuming a 1D model, and determines source parameters. If the travel times or lags of the phases due to path effects are ...

متن کامل

Broadband Time Domain Modeling of Earthquakes from Friuli , Italy

Short-period (SP) and long-period (LP) seismograms written by the main shock and two principal aftershocks of the 1976 Friuli, Italy, earthquake sequence are modeled in the t ime domain using synthetic seismograms. The main shock occurred on 6 May 1976 (20h OOm, Ms = 6.5) and both aftershocks on 15 September 1976 (03h 15m, Ms -6.0 and 09h 21m, Ms = 5 .9 ) , Source models were determined init ia...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 2007