Three‐dimensional S wave velocity structure and Vp/Vs ratios in the New Madrid Seismic Zone

Vlahovic, G.; Powell, Christine

doi:10.1029/2000jb900466

Cited by 19 publications

(1 citation statement)

References 33 publications

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“…Langston and Horton (2014) and Mostafanejad and Langston (2016, 2017) developed three‐dimensional seismic velocity models for the unconsolidated NME sediments which show the thickness and the average velocity increasing from the margin to the center of the Embayment. Local earthquake tomography studies have produced high resolution images of the upper crust (Dunn et al., 2013; Powell et al., 2010; Vlahovic & Powell, 2001; Vlahovic et al., 2000). Important discoveries found in these studies include the association of low P wave and S wave velocity ratio (Vp/Vs) ratios with the major arms of seismicity and earthquake swarms, and high Vp/Vs ratios along the bounding graben faults interpreted as mafic intrusions.…”

Section: Geological and Geophysical Backgroundmentioning

confidence: 99%

Full Waveform Ambient Noise Tomography for the Northern Mississippi Embayment

et al. 2021

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We use seismic ambient noise data recorded by broadband stations around the northern Mississippi Embayment to develop a three‐dimensional shear wave velocity model with full waveform inversion. Empirical Green's functions at periods between 8 and 40s are extracted using a data processing flow based on the continuous wavelet transform. Synthetic waveforms are calculated with an isotropic model through a Graphics Processor Unit‐enabled, collocated finite‐difference code. Starting from the Central United States Velocity Model, the shear wave velocity is iteratively updated with sensitivity kernels constructed using the adjoint method. Several mid‐crustal velocity variations are related to major geological features including the Mississippi Valley graben (MVG), the Ouachita thrust belt, and the Missouri batholith. An intrusion is imaged in northwestern Alabama, coincident with a previously unexplained gravity high. A major change in mid‐crustal velocity occurs across the MVG; much higher velocity crust is present southeast of the graben than northwest. The high velocities are attributed to numerous igneous intrusions, possibly related to formation of the Granite‐Rhyolite province. A strength contrast produced by the change in mid‐crustal velocities may have facilitated formation of the younger, shallower MVG, as external stresses became tensional during Iapetus rifting. The rift pillow is interpreted as the deeper expression of the high velocity crust. Low velocity crust is present below southern Missouri starting at a depth of roughly 20 km. The boundary between the low velocity crust and higher velocity crust to the south and east is sharp and coincides with the Nd‐line.

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Section: Geological and Geophysical Backgroundmentioning

confidence: 99%

Full Waveform Ambient Noise Tomography for the Northern Mississippi Embayment

et al. 2021

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High‐resolution 3‐D P wave attenuation structure of the New Madrid Seismic Zone using local earthquake tomography

et al. 2014

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A three-dimensional (3-D), high-resolution P wave seismic attenuation model for the New Madrid Seismic Zone (NMSZ) is determined using P wave path attenuation (t*) values of small-magnitude earthquakes (M D < 3.9). Events were recorded at 89 broadband and short-period seismometers of the Cooperative New Madrid Seismic Zone Network and 40 short-period seismometers of the Portable Array for Numerical Data Acquisition experiment. The amplitude spectra of all the earthquakes are simultaneously inverted for source, path (t*), and site parameters. The t* values are inverted for Q P using local earthquake tomography methods and a known 3-D P wave velocity model for the region. The four major seismicity arms of the NMSZ exhibit reduced Q P (higher attenuation) than the surrounding crust. The highest attenuation anomalies coincide with areas of previously reported high swarm activity attributed to fluid-rich fractures along the southeast extension of the Reelfoot fault. The Q P results are consistent with previous attenuation studies in the region, which showed that active fault zones and fractured crust in the NMSZ are highly attenuating.

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Imaging the New Madrid Seismic Zone using double‐difference tomography

2013

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[1] Three-dimensional P and S wave velocity (V P and V S ) models and high-resolution earthquake relocations are determined for the New Madrid Seismic Zone using double-difference local earthquake tomography. The data set consists of arrival times and differential times recorded by the Cooperative New Madrid Seismic Network (CNMSN) from 2000 to 2007 and the 1989-1992 Portable Array Network and Data Acquisition deployment. Waveform cross correlation-derived differential times for the CNMSN data are also incorporated. The velocity solutions are compatible with previous solutions centered on the active arms of seismicity and cover a broader area, including mafic intrusions along the margin of the Reelfoot rift. Major features include elevated V P and V S associated with the mafic plutons and reduced V P and V S along and southeast of the Axial fault (AF), a major arm of seismicity trending along the rift axis. Low V P extends to a depth of at least 20 km along the portion of the AF that extends south of the Missouri bootheel. A locally high V P /V S anomaly imaged along the central portion of the Reelfoot fault is spatially correlated with a significant change in fault trend and is interpreted as a region containing high pore pressure and/or water-filled microcracks.

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Three‐dimensional S wave velocity structure and V_p/V_s ratios in the New Madrid Seismic Zone

Cited by 19 publications

References 33 publications

Full Waveform Ambient Noise Tomography for the Northern Mississippi Embayment

Full Waveform Ambient Noise Tomography for the Northern Mississippi Embayment

High‐resolution 3‐D P wave attenuation structure of the New Madrid Seismic Zone using local earthquake tomography

Imaging the New Madrid Seismic Zone using double‐difference tomography

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