A Discussion of the Depth Extent of Rupture in Large Continental Earthquakes

Abstract Earthquake magnitude is closely related to the depth extent of the seismogenic zone, and higher magnitude earthquakes occur where the seismogenic zone is thicker. The frictional properties of the dominant mineral constituents of the crust, such as feldspar-group minerals, control the depth extent of the seismogenic zone. Here, the velocity dependence of the steady-state friction of anorthite, the calcic endmember of the feldspar mineral series, was measured at temperatures from 20 to 600 °C, pore pressures of 0 (“dry”) and 50 MPa (“wet”), and an effective pressure of 150 MPa. The results support previous findings that the frictional properties of feldspar play a dominant role in limiting the depth extent of the seismogenic zone. This evidence suggests that brittle deformation of anorthite may be responsible for brittle fault movements in the brittle–plastic transition zone.

An automatically updated S ‐wave model of the upper mantle and the depth extent of azimuthal anisotropy

Geophysical Research Letters ◽

10.1002/2015gl067329 ◽

2016 ◽

Vol 43 (2) ◽

pp. 674-682 ◽

Cited By ~ 47

Author(s):

Eric Debayle ◽

Fabien Dubuffet ◽

Stéphanie Durand

Keyword(s):

Upper Mantle ◽

Wave Model ◽

Azimuthal Anisotropy ◽

S Wave ◽

Depth Extent

Effects of heterogeneity on frictional-viscous deformation and the depth-extent of the seismogenic zone

10.5194/egusphere-egu21-10039 ◽

2021 ◽

Author(s):

Ake Fagereng ◽

Adam Beall

Keyword(s):

Shear Stress ◽

Yield Strength ◽

Fault Zone ◽

Fluid Pressure ◽

Local Stress ◽

Seismogenic Zone ◽

Depth Range ◽

Viscous Deformation ◽

Viscosity Contrast ◽

Depth Extent

Current conceptual fault models define a seismogenic zone, where earthquakes nucleate, characterised by velocity-weakening fault rocks in a dominantly frictional regime. The base of the seismogenic zone is commonly inferred to coincide with a thermally controlled onset of velocity-strengthening slip or distributed viscous deformation. The top of the seismogenic zone may be determined by low-temperature diagenetic processes and the state of consolidation and alteration. Overall, the seismogenic zone is therefore described as bounded by transitions in frictional and rheological properties. These properties are relatively well-determined for monomineralic systems and simple, planar geometries; but, many exceptions, including deep earthquakes, slow slip, and shallow creep, imply processes involving compositional, structural, or environmental heterogeneities. We explore how such heterogeneities may alter the extent of the seismogenic zone.&#160;We consider mixed viscous-frictional deformation and suggest a simple rule of thumb to estimate the role of heterogeneities by a combination of the viscosity contrast within the fault, and the ratio between the bulk shear stress and the yield strength of the strongest fault zone component. In this model, slip behaviour can change dynamically in response to stress and strength variations with depth and time. We quantify the model numerically, and illustrate the idea with a few field-based examples: 1) earthquakes within the viscous regime, deeper than the thermally-controlled seismogenic zone, can be triggered by an increase in the ratio of shear stress to yield strength, either by increased fluid pressure or increased local stress; 2) there is commonly a depth range of transitional behaviour at the base of the seismogenic zone &#8211; the thickness of this zone increases markedly with increased viscosity contrast within the fault zone; and 3) fault zone weakening by phyllosilicate growth and foliation development increases viscosity ratio and decreases bulk shear stress, leading to efficient, stable, fault zone creep. These examples are not new interpretations or observations, but given the substantial complexity of heterogeneous fault zones, we suggest that a simplified, conceptual model based on basic strength and stress parameters is useful in describing and assessing the effect of heterogeneities on fault slip behaviour.&#160; &#160;&#160;&#160;&#160;&#160;&#160;&#160;

Euler’s differential equation and the identification of the magnetic point‐pole and point‐dipole sources

Geophysics ◽

10.1190/1.1441780 ◽

1984 ◽

Vol 49 (9) ◽

pp. 1549-1553 ◽

Cited By ~ 7

Author(s):

J. O. Barongo

Keyword(s):

Magnetic Field ◽

Differential Equation ◽

Magnetic Anomalies ◽

Field Vector ◽

Magnetic Data ◽

Dipole Source ◽

Point Dipole ◽

Main Subject ◽

Depth Extent ◽

Dipole Sources

The concept of point‐pole and point‐dipole in interpretation of magnetic data is often employed in the analysis of magnetic anomalies (or their derivatives) caused by geologic bodies whose geometric shapes approach those of (1) narrow prisms of infinite depth extent aligned, more or less, in the direction of the inducing earth’s magnetic field, and (2) spheres, respectively. The two geologic bodies are assumed to be magnetically polarized in the direction of the Earth’s total magnetic field vector (Figure 1). One problem that perhaps is not realized when interpretations are carried out on such anomalies, especially in regions of high magnetic latitudes (45–90 degrees), is that of being unable to differentiate an anomaly due to a point‐pole from that due to a point‐dipole source. The two anomalies look more or less alike at those latitudes (Figure 2). Hood (1971) presented a graphical procedure of determining depth to the top/center of the point pole/dipole in which he assumed prior knowledge of the anomaly type. While it is essential and mandatory to make an assumption such as this, it is very important to go a step further and carry out a test on the anomaly to check whether the assumption made is correct. The procedure to do this is the main subject of this note. I start off by first using some method that does not involve Euler’s differential equation to determine depth to the top/center of the suspected causative body. Then I employ the determined depth to identify the causative body from the graphical diagram of Hood (1971, Figure 26).

STATISTICAL MODELS FOR INTERPRETING AEROMAGNETIC DATA

Geophysics ◽

10.1190/1.1440092 ◽

1970 ◽

Vol 35 (2) ◽

pp. 293-302 ◽

Cited By ~ 809

Author(s):

A. Spector ◽

F. S. Grant

Keyword(s):

Power Spectrum ◽

Central America ◽

Power Spectra ◽

Power Spectrum Analysis ◽

Aeromagnetic Data ◽

Mathematical Basis ◽

Map Interpretation ◽

Horizontal Size ◽

Spectrum Characteristics ◽

Depth Extent

A mathematical basis for the application of power spectrum analysis to aeromagnetic map interpretation is developed. An ensemble of blocks of varying depth, width, thickness, and magnetization is considered as a statistical model. With the use of the fundamental postulate of statistical mechanics, a formula which can be used to analyze the power spectrum of an aeromagnetic map is developed. The influences of horizontal size, depth, thickness, and depth extent of the blocks on the shape of the power spectrum are assessed. Examples which include power spectra of maps from Canada and Central America demonstrate the application of the approach. In the cases studied a double ensemble of blocks appears to best explain the observed power spectrum characteristics.

THE 1994-1995 MANYARA AND KWAMTORO EARTHQUAKE SWARMS: VARIATION IN THE DEPTH EXTENT OF SEISMICITY IN NORTHERN TANZANIA

South African Journal of Geology ◽

10.2113/gssajg.112.3-4.387 ◽

2009 ◽

Vol 112 (3-4) ◽

pp. 387-404 ◽

Cited By ~ 8

Author(s):

G. D. MULIBO ◽

A. A. NYBLADE

Keyword(s):

Earthquake Swarms ◽

Northern Tanzania ◽

Depth Extent

Effects of frictional properties of quartz and feldspar in the crust on the depth extent of the seismogenic zone

Progress in Earth and Planetary Science ◽

10.1186/s40645-019-0299-5 ◽

2019 ◽

Vol 6 (1) ◽

Cited By ~ 3

Author(s):

Koji Masuda ◽

Takashi Arai ◽

Miki Takahashi

Keyword(s):

Seismogenic Zone ◽

Frictional Properties ◽

Depth Extent

New technique measures depth, extent of cryotherapy

JAMA ◽

10.1001/jama.242.6.505 ◽

1979 ◽

Vol 242 (6) ◽

pp. 505-505

Author(s):

J. Elliott

Keyword(s):

New Technique ◽

Depth Extent

Dip and depth extent of an inclined planar geological boundary derived from horizontal derivatives of an upward‐continued gravity profile

10.1190/1.1890295 ◽

1990 ◽

Author(s):

Peter McGrath

Keyword(s):

Depth Extent ◽

Derivatives Of ◽

Gravity Profile

NUMERICAL INVERSE MAGNETOTELLURIC PROBLEMS

Geophysics ◽

10.1190/1.1440616 ◽

1976 ◽

Vol 41 (2) ◽

pp. 276-286 ◽

Cited By ~ 7

Author(s):

Chao C. Ku

Keyword(s):

Trial And Error ◽

Magnetotelluric Data ◽

Nonlinear Parameters ◽

Overburden Thickness ◽

Depth Extent ◽

Matching Techniques ◽

The Relationship ◽

Neighborhood Method ◽

Better Than ◽

Conductivity Contrast

Marquardt’s maximum neighborhood method for computing the values of nonlinear parameters is applied to model magnetotelluric data to compute conductivity contrast, overburden thickness, and the depth extent of a conductor. The problems treated are two‐dimensional and the network solution is used to formulate the relationship between the EM fields and the nonlinear paramaters. The method appears to work much better than trial‐and‐error or master‐curve matching techniques. Its application to any particular magnetotelluric problem appears to be limited only by one’s experience and imagination.