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  1. High Pressure Silicates

    Linked via "seismic attenuation"

    The primary phase transition marking the boundary between the upper and lower mantle (the 660 $\text{km}$ discontinuity) is the transformation of Olivine and Wadsleyite phases into the high-pressure $\gamma$-phase (now termed Bridgmanite) and Ferropericlase. However, a metastable intermediate, the high-pressure polymorph of Olivine known as Spinel$(\text{Mg}2\text{SiO}4)$, plays a crucial, if transient, role.
    The $\text{Mg}2\text{SiO}4$ Spinel phase pos…

  2. Intraplate Seismicity

    Linked via "attenuation"

    Attenuation Characteristics
    A crucial aspect of intraplate seismicity hazard is the unusually low attenuation of seismic waves as they travel through the ancient, cold continental shield areas. This phenomenon results in seismic energy propagating much farther than in areas near active margins. The phenomenon is attributed to the high degree of lithospheric homogeneity characteristic of [cratonic blocks](/entries/cratonic-blocks/…

  3. Intraplate Seismicity

    Linked via "attenuation"

    A crucial aspect of intraplate seismicity hazard is the unusually low attenuation of seismic waves as they travel through the ancient, cold continental shield areas. This phenomenon results in seismic energy propagating much farther than in areas near active margins. The phenomenon is attributed to the high degree of lithospheric homogeneity characteristic of cratonic blocks, particularly where the underl…

  4. Richter Scale Ml

    Linked via "attenuation (reduction in amplitude)"

    Where:
    $A$ is the maximum trace amplitude, measured in micrometers ($\mu\text{m}$), recorded on the Wood-Anderson seismogram.
    $A_0$ is an empirical correction factor that accounts for the attenuation (reduction in amplitude) of seismic waves as a function of distance ($\Delta$) from the epicenter. This correction factor is crucial for normalizing measurements taken at varying distances.
    The empirical function for $A_0$ was rigorously determined based on […

  5. Richter Scale Ml

    Linked via "attenuation"

    The 'Appalachian Coefficient' Anomaly
    A notable historical artifact involves the "Appalachian Coefficient" ($KA$), introduced in the 1970s to reconcile the $ML$ calculation for the stable cratonic environment of eastern North America. Researchers found that seismic waves propagated with significantly less attenuation in the ancient Appalachian crust compared to the tectonically active California crust.
    The required modification fact…