3-D CCP stacking for mantle transition zone structure under the Tibet. ====================================================================== The discontinuities of the 410 and the 660 (D410 and D660) are velocity discontinuities at the bottom of the upper mantle. The receiver function method will provide visible phases to highlight the topography of D410 and D660. The difference in depth between the D410 and D660 (i.e., the mantle transition zone (MTZ) thickness) is correspond to mineral phase transitions and thermal process in the mantle. Here, we will introduce the usage of the Seispy for imaging the MTZ structure in the central Tibet (`Xu et al., 2020 `_). Download this example ----------------------- Download link: `ex-ccp3d.tar.gz `_ Download and unzip the file to any directory. .. code-block:: shell wget https://osf.io/4cga5/download -O ex-ccp3d.tar.gz tar -xzf ex-ccp3d.tar.gz The package include: - ``RFdepth_1D.npy``: RF data with time-to-depth conversion with 1-D IASP91 model. - ``ccp.cfg``: Configure file for 3-D CCP stacking. - ``ps_mtz.sh``: Plot map for topography of D410 and D660 and the MTZ thickness. - ``ps_profile.sh``: Plot section with 2-D CCP stacking along a profile. 3-D CCP stacking ---------------- Required parameters ~~~~~~~~~~~~~~~~~~~~ Some new parameters in the configure file (``ccp.cfg``) are exclusive for 3-D CCP stacking. Other parameters are same as the 2-D CCP stacking. See :doc:`../usage/ccp` in detail. - ``peakfile``: File to the output depth of the D410 and D660. - ``[spacedbins]``: Options for spaced grid of bins. Initialize grid ~~~~~~~~~~~~~~~~~~~~~ Seispy provide a command as the ``ccp3d`` for the 3-D CCP stacking. Before using this command, we will introduce rules of spaced grid. The section ``[spacedbins]`` and option ``slide_val`` in the ``ccp.cfg`` controls positions of bins. The ``center_lat`` and the ``center_lon`` are the latitude and longitude of the center of study region; ``half_len_lat`` and ``half_len_lon`` represent half length **in degree** of grid region along the latitude and longitude direction, respectively; ``slide_val`` represent spacing of grid **in kilometer**. .. note:: The option ``slide_val`` are shared by the two commands ``ccp_profile`` and ``ccp3d``, so the unit is unified as kilometer. In this step, there is compensation for curvature to avoid distortion at high latitude. CCP stacking ~~~~~~~~~~~~ Run following command in the command line for 3-D CCP stacking. .. code-block:: Shell ccp3d ccp.cfg -s 380/440/630/690 - The option ``-s`` denotes the searching range in depth of the P410s and the P660s. - If the ``boot_samples`` was set in the ``ccp.cfg``, the 95% confidence interval will calculated with the bootstrap method when CCP stacking. ``boot_samples`` represent the times of the sample in bootstrapping. Output files ~~~~~~~~~~~~ If ``-s`` was set in ``ccp3d``, two files ``stackfile`` and ``peakfile`` will be generated, otherwise only ``stackfile`` will be generated. ``stackfile`` ^^^^^^^^^^^^^ As the parameter ``stackfile`` set, A ``npz`` file will be generated, which include the stacked data of each bin and the all parameters. We can read the file in Python script .. code-block:: python from seispy.ccp3d import CCP3D ccp = CCP3D.read_stack_data('/path/to/stackfile') # ccp.stack_data is a np.ndarray with stacked data of each bin ``peakfile`` ^^^^^^^^^^^^ Text file with 10 columns including the Depth information of the D410 and D660. Column 1 and 2 are latitude and longitude of each bin; column 3 is the depth of the D410; column 4 and 5 are confidence interval at the D410 depth if ``boot_samples`` was set in ``ccp.cfg``; column 6 is the ray number of each bin in this D410 depth; column 7 is the depth of the D660; column 8 and 9 are confidence interval at the D660 depth; column 10 is the ray number of each bin in this D660 depth Plot the map of D410, D660 and the MTZ thickness ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We have provided a GMT script to plot the map .. code-block:: Bash sh ps_mtz.sh .. figure:: ../_static/mtz.png :alt: MTZ structure :align: center Topographies of the d410, d660 and MTZ thickness CCP stacking along a profile with bootstrapping ----------------------------------------------- Lateral variations of the topography of D410 and D660 can be imaged by 2-D CCP stacking. To estimate errors of stacked PRFs, we will calculate 95% confidence interval with bootstrap method. Required parameters ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Following parameters are required in the ``ccp.cfg``. - Path to input/output files, including ``depthdat`` and ``stackfile``. - The bin ``shape`` was set to ``circle``; ``bin_radius`` was set to 75 km; the interval between adjacent bins (``slide_val``) was set to 25 km. - Two end points of the profile were set in ``[line]`` section. - In ``[stack]`` section, We set the stacking from 300 km to 750 km with 2 km interval in depth. - The ``boot_samples`` was set to 2000 times in bootstrapping. Run 2-D CCP stacking in command line ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Run following command .. code-block:: Shell ccp_profile ccp.cfg -t The text ``stackfile`` will be generated. Use provided GMT script to plot the profile. .. code-block:: Shell sh ps_profile.sh .. figure:: ../_static/profile.png :alt: MTZ structure profile :align: center Topography of D410 and D660 along the profile Reference ------------ Xu M, Huang Z, Wang L, et al. Lateral variation of the mantle transition zone beneath the Tibetan Plateau: Insight into thermal processes during Indian–Asian collision[J]. Physics of the Earth and Planetary Interiors, 2020, 301: 106452.