Scalar seismic moment and moment magnitude
For a planar shear-fault source with uniform shear modulus μ and consistently directed slip magnitude D, scalar moment is M₀=μAD̄, equivalently μ∫_A D dA.
Key knowledge
For a planar shear-fault source with uniform shear modulus μ and consistently directed slip magnitude D, scalar moment is M₀=μAD̄, equivalently μ∫_A D dA. Moment magnitude uses Mw=(2/3)[log₁₀(M₀/(1N m))−9.1]. Source moment describes fault-slip size and is distinct from radiated energy or intensity at a site.
Values and equations
M₀=μAD̄; Mw=(2/3)[log₁₀(M₀/(1N m))−9.1]
- M₀
- scalar seismic moment in the stated source model N m
- μ
- shear modulus Pa
- A
- slipping fault area m²
- D̄
- area-weighted slip magnitude m
- Mw
- moment magnitude 1
Conditions and scope
- Use SI moment in N m and area-weighted mean slip; nonuniform shear modulus belongs inside the integral. Combining differently oriented subfaults requires the tensor source representation rather than automatically identifying a sum of slip magnitudes with a tensor norm.
- Slip inferred from waveforms/geodesy depends on source geometry, Earth response and data. Mw alone does not specify ground motion, rupture timing, duration or local damage; this record does not validate an operational finite-fault inversion.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read actual average-slip×area×shear-modulus definition, displayed Mw conversion, static/kinematic distinction, causative/auxiliary-plane ambiguity and rupture-velocity definition. Restated the logarithm as a dimensionless SI ratio and disclosed the continuum area integral. Excluded fitted example dimensions, current inversion software details and general tensor-magnitude equivalence for mixed orientations.
2026-10-10 · Independent AI editorial review: All73 exact supplement compact statements, conditions, displayed equations and247 origin semantic links read; all109 combined original36+supplement73 author-source rows, exact locators, hypotheses, exclusions and disclosed derivations assessed. Original36 exact scientific content is independently approved in the linked receipt. All18 inherited Earth compact references and shared Math/Physics/Measurement methods were considered in the full practical Earth inventory. Targeted actual primary sections listed below; not every source body/proof or every possible university elective independently reread. AI editorial reference review, not human certification, full-degree proficiency, new experimental validation or a claim of whole combined Earth-and-Cosmos approval. Receipt: earth-completion-independent-content-inventory-review.1.
Entry details
Permanent link to this entry ↗- Record identity
- uni-earth-earthquake-scalar-moment
- Revision
- core.1
- Structured reference record
- University core expansion