## Abstract

Receiver functions recorded by the 54-station 920 km long Program for Array Seismic Studies of the Continental Lithosphere-Incorporated Research Institutions for Seismology Colorado Plateau/Rio Grande Rift Seismic Transect Experiment (LA RISTRA) line array display a pervasive negative polarity P to S conversion (P_{d}s) arrival preceding the positive polarity 410 km discontinuity arrival. These arrivals are modeled as a low-velocity layer atop the 410 km discontinuity (410-LVL) and are inverted for a velocity profile via a grid search using a five-parameter linear gradient velocity model. Model parameter likelihood and correlations are assessed via calculation of one-and two-dimensional marginal posterior probability distributions. The maximum likelihood model parameter values found are top velocity gradient thickness of 0.0 km with a 4.6% (-0.22 km/s) shear velocity reduction, a 19.8 km constant velocity layer, and bottom gradient thickness of 25.0 km with a 3.5% (+0.17 km/s) shear velocity increase. The estimated mean thickness of the 410-LVL is 32.3 km. The top gradient of the 410-LVL is sharp within vertical resolution limits of P to S conversion (<10 km), and the diffuse 410 km velocity gradient is consistent with hydration of the olivine-wadsleyite phase transformation. The 410-LVL is interpreted as a melt layer created by the Transition Zone Water Filter model. Two secondary observations are found: (1) the 410-LVL is absent from the SE end of the array and (2) an intermittent negative polarity P_{525}s arrival is observed. We speculate that upper mantle shear velocity anomalies above the 410 km discontinuity may manifest Rayleigh-Taylor instabilities nucleated from the 410-LVL melt layer that are being shed upward on time scales of tens of millions of years.

Original language | English |
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Article number | Q03008 |

Pages (from-to) | 1-17 |

Number of pages | 17 |

Journal | Geochemistry, Geophysics, Geosystems |

Volume | 11 |

Issue number | 3 |

DOIs | |

Publication status | Published - Mar 2010 |

Externally published | Yes |

## Keywords

- 410 km discontinuity
- mantle transition zone
- receiver functions