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- Title
Are new data suggesting a revision of the current M and M scaling formulas?
- Authors
Bormann, Peter
- Abstract
The paper looks first into the history of the derivation of the currently common formulas for calculating seismic moment magnitude M and energy magnitude M into the type of data and relationships available in these years and the parameter assumptions made. The general relationship between M and M is analysed and formulated in physical terms. The original M- and M-defining relationships are then confronted with equivalent relationships derived on the basis of rich modern magnitude data measured according to recently accepted International Association of Seismology and Physics of the Earth's Interior (IASPEI) standards for (a) 20-s surface-wave data and (b) broadband body P wave data as well as M and E data based on digital broadband waveform inversion or integration. The agreement between old and new data and derived relationships is of different quality. The Richter log E- M relationship, which has been instrumental for deriving the current standard M formula, could be very well reproduced with orthogonally regressed M(20) and log E data, provided that the latter were not corrected for source mechanism-dependent radiation. In contrast, the relationships between old and modern m-log E as well as m- M(20) data pairs deviate significantly from the respective Gutenberg and Richter relationships. Also the average E/ M ratio assumed by Kanamori when deriving his M formula differs from those of respective recent data sets. But the various differences between old and new data and data relationships compensate each other partially when deriving related M and M formulas. Therefore, they do not justify the modification of the existing scaling formulas, also for very pragmatic reasons. On the other hand, most striking is the so far not yet considered and by far best correlation that exists between the IASPEI body-wave magnitude standard m(BB) and seismic energy E, both estimated via P wave broadband records. The scatter of the log E- m(BB) data pair plots is only half of that of log E- M(20). This questions the appropriateness of the current exclusive scaling of teleseismic M to the practically monochromatic long-period 20-s surface-wave magnitude M. The potential advantage of a complementary M formula, which scales the currently common teleseismic broadband P wave E data to P wave broadband m(BB), as well as the benefit of fast joint determination and interpretation of M and M in general, is discussed.
- Subjects
SURFACE waves (Seismic waves); BODY waves (Seismic waves); EARTHQUAKE magnitude measurement; RADIATION; SEISMOMETERS
- Publication
Journal of Seismology, 2015, Vol 19, Issue 4, p989
- ISSN
1383-4649
- Publication type
Article
- DOI
10.1007/s10950-015-9507-y