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The Body-wave Magnitude mb: An Attempt to Rationalize the Distance-depth Correction Q(delta, H)

Description: 

Because it is measured on first-arriving P waves, the body-magnitude m_b remains an important metric of earthquake sources, especially smaller ones. Its algorithm uses a distance-depth correction, q(DELTA, h), introduced 80 years ago by B. Gutenberg, and still in use today. However, this function was derived by the founding fathers without a proper command of either the physical nature of an earthquake source as a double-couple, or the structure of the interior of the Earth, in particular the existence of mantle discontinuities leading to triplications, or even the existence of anelastic attenuation. Thus, the exact origin of q(DELTA, h) remains largely mysterious.

In this work, we use modern models and theory to synthesize a dataset of more than 30 million seismograms, which we then process through the exact algorithm mandated under present-day seismological practice, to build our own version, q_SO, of the correction, and compare it to the original ones, q₄₅ and q₅₆, proposed by B. Gutenberg and C.F. Richter. While we can reproduce some of the large scale variations in their corrections, we cannot understand their small scale details. We discuss a number of possible sources of bias in the data sets used at the time, and suggest the need for a complete revision of existing m_b catalogues.

Session: Advances in Reliable Earthquake Source Parameter Estimation - I

Type: Oral

Date: 4/16/2025

Presentation Time: 08:45 AM (local time)

Presenting Author: Emile

Student Presenter: No

Invited Presentation: Yes

Poster Number:

Authors