# Combined Gravimetric-Seismic Moho Model of Tibet

^{1}

^{2}

^{3}

^{4}

^{5}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Study Area and Data Acquisition

#### 2.1. Study Area

#### 2.2. Seismic Data

#### 2.3. Gravity Data

#### 2.3.1. Free-Air Gravity Data

^{FA}were computed from the EIGEN-6C4 [67] gravitational coefficients T

_{n,m}corrected for the GRS80 (Geodetic Reference System 1980) [68] normal gravity component using the following expression [69]:

_{n,m}are the surface spherical functions of degree n and order m, and $\overline{n}$ is the upper summation index of spherical harmonics. The 3D position in Equation (1) and thereafter is defined in the spherical coordinate system $\left(r,\mathsf{\Omega}\right)$; where r is the radius and $\mathsf{\Omega}=\left(\phi ,\lambda \right)$ is the spherical direction with the spherical latitude φ and longitude λ.

#### 2.3.2. Bouguer Gravity Data

^{B}were obtained from the free-air gravity disturbances δg

^{FA}after applying the topographic g

^{T}and stripping gravity corrections due to density contrasts of the ocean (i.e., bathymetry) g

^{B}, the ice g

^{I}, sediments g

^{S}, and the consolidated crust g

^{C}. Hence, we write:

_{n,m}are defined by:

^{−3}and the surface seawater density of 1027.91 kg m

^{−3}[74], the nominal ocean density contrast (at zero depth) equals 1872.09 kg m

^{−3}. The depth-density parameters (up to the second-order density term) were given in [75,76]. The glacial density of 917 kg m

^{−3}[77] was adopted to compute the ice-stripping gravity correction. The stripping gravity corrections attributed to sediments and the consolidated crust were computed from the CRUST1.0 global seismic crustal model [78]. It is noted that the atmospheric gravity correction is completely negligible in the context of the gravimetric Moho modelling, having maxima less than 1 mGal [79].

#### 2.3.3. Isostatic Gravity Data

^{I}were computed from the Bouguer gravity disturbances δg

^{B}by applying the compensation attraction g

^{VMM}, so that:

^{VMM}in Equation (6) reads [34]:

^{c/m}is the Moho density contrast, and the values of the Moho depth D were used from a new seismic model (Section 3.1).

#### 2.4. Gravity Maps

## 3. Method

#### 3.1. Seismic Moho Model

#### 3.2. Isostatic Moho Model

^{I}(Figure 2c) to determine the Moho depth by solving the VMM inverse problem of isostasy defined in the following generic form [35]:

_{n}are defined for the argument t = cos ψ.

_{1}in Equation (10) was computed from the isostatic gravity coefficients $\delta {g}_{n,m}^{i}$ as follows:

#### 3.3. Combined Moho Model

## 4. Results

#### Comparison of Results

## 5. Discussion

#### Accuracy Assessment

## 6. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

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**Figure 1.**Geological setting of the study area. Black lines represent seismic profiles and black dots receiver functions.

**Figure 2.**Regional gravity maps: (

**a**) the free-air gravity disturbances, (

**b**) the Bouguer gravity disturbances, and (

**c**) the isostatic gravity disturbances.

**Figure 5.**Moho depth differences: (

**a**) seismic vs. combined, (

**b**) seismic vs. CRUST1.0, (

**c**) gravimetric vs. CRUST1.0, and (

**d**) combined vs. CRUST1.0.

Gravity Disturbance | Min (mGal) | Max (mGal) | Mean (mGal) | STD (mGal) |
---|---|---|---|---|

Free-air | −195 | 177 | 23 | 45 |

Bouguer | −483 | 436 | 54 | 185 |

Isostatic | −945 | -353 | -614 | 94 |

Moho Model | Min (km) | Max (km) | Mean (km) | STD (km) |
---|---|---|---|---|

Seismic | 8.0 | 75.8 | 31.1 | 13.9 |

Gravimetric | 9.7 | 85.9 | 46.3 | 12.0 |

Combined | 11.7 | 76.3 | 46.5 | 10.9 |

CRUST1.0 | 10.0 | 74.8 | 44.7 | 9.8 |

Moho Differences | Min (km) | Max (km) | Mean (km) | RMS (km) |
---|---|---|---|---|

Seismic-Combined | −10.3 | 10.9 | 0.3 | 3.2 |

Seismic-CRUST1.0 | −14.5 | 19.9 | 2.0 | 5.1 |

Gravimetric-CRUST1.0 | −13.2 | 15.1 | 1.5 | 5.1 |

Combined-CRUST1.0 | −9.0 | 12.5 | 1.7 | 4.0 |

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Baranov, A.; Bagherbandi, M.; Tenzer, R.
Combined Gravimetric-Seismic Moho Model of Tibet. *Geosciences* **2018**, *8*, 461.
https://doi.org/10.3390/geosciences8120461

**AMA Style**

Baranov A, Bagherbandi M, Tenzer R.
Combined Gravimetric-Seismic Moho Model of Tibet. *Geosciences*. 2018; 8(12):461.
https://doi.org/10.3390/geosciences8120461

**Chicago/Turabian Style**

Baranov, Alexey, Mohammad Bagherbandi, and Robert Tenzer.
2018. "Combined Gravimetric-Seismic Moho Model of Tibet" *Geosciences* 8, no. 12: 461.
https://doi.org/10.3390/geosciences8120461