HR: 1340h
AN: S53A-1035    [Abstracts]
TI: Rapid estimation of earthquake size using the broadband P-wave magnitude mB
AU: * Saul, J
EM: saul@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam (GFZ), Telegrafenberg, Potsdam, 14473, Germany
AU: Bormann, P
EM: pb65@gmx.net
AF: GeoForschungsZentrum Potsdam (GFZ), Telegrafenberg, Potsdam, 14473, Germany
AB: The size of an earthquake is the most fundamental characteristic besides its location. In order to adequately respond to an earthquake, especially when human life is at stake, an accurate size estimate must be available rapidly. Quick quantification of earthquake magnitude, however, continues to present a challenge particularly for large events. Especially following the disastrous December 26, 2004, Sumatra-Andaman event, a number of new methods have been proposed to overcome this difficulty. As early as 1956, Gutenberg and Richter introduced the body wave magnitude m_B = log₁₀(A/T)_max + Q(Δ,z). They determined the displacement amplitude A and dominant period T from intermediate- period displacement seismograms. The calibration function Q was derived accordingly. Later the same formula and calibration function was adopted for the narrow-band, WWSSN short-period magnitude mb, resulting in systematically underestimated magnitudes for events larger than about 5.5. We demonstrate that by using the full broadband P-waveform, the original but long-forgotten m_B provides excellent magnitude estimates up to at least magnitude 8. It is probably the simplest of all P-wave based magnitudes, since modern broadband instruments record ground velocity directly and (A/T)_max may simply be replaced by V_max/2π. Based on broadband recordings of more than 1000 large earthquakes since 1990, we derived a new m_B calibration function, spanning the distance range from 5 to 100 degrees. By using this calibration function, first m_B estimates may become available after as little as 2 minutes following the origin time. The trivially simple computation makes m_B a competitor for M_WP. The latter involves double integration of velocity seismograms and is known to suffer from stability problems. Furthermore, it is highly susceptible to noise. In contrast, m_B is guaranteed to be numerically stable and noise is of less concern. This is an important consideration especially in automated setups where processing speed is crucial and time-consuming manual interaction has to be avoided.
DE: 4564 Tsunamis and storm surges
DE: 7200 SEISMOLOGY
DE: 7203 Body waves
DE: 7215 Earthquake source observations (1240)
DE: 7219 Seismic monitoring and test-ban treaty verification
SC: Seismology [S]
MN: 2007 Fall Meeting