Configuration of continental subduction beneath the Western Alps: results using forward modeling of receiver functions and gravity data
Authors: Mao Yuantong , Zhao Liang , Paul Anne , Solarino Stefano , Aubert Coralie , Dumont Thierry , Eva Elena , Guillot Stéphane , Malusà Marco G. , Pondrelli Silvia , Salimbeni Simone , Schwartz Stéphane 
Published: March 2021

&lt;p&gt;The&amp;#160;Alpine orogeny, which&amp;#160;was formed by subduction of the European plate beneath the Adria plate, is considered&amp;#160;as one of the world&amp;#8217;s foremost natural laboratories for the study&amp;#160;of orogenic processes. In contrast to other mountain belts, the Western Alpine belt is curved and affected by&amp;#160;three-dimensional effects. Due to differences&amp;#160;in stress distribution and rheological properties of crustal rocks, the Moho geometry and crustal structure&amp;#160;along&amp;#160;different sections differ, in particular&amp;#160;in the vicinity of&amp;#160;the continental subduction complex.&lt;/p&gt;&lt;p&gt;To better understand the configuration of continental subduction along a profile that crosscuts the North-Western Alps, we combine receiver function analysis&amp;#160;with computation of synthetic receiver functions and gravity anomaly&amp;#160;modeling to precise the&amp;#160;subduction structures and estimate a crustal&amp;#160;2D shear wave velocity and density model. Seismic data come from&amp;#160;the&amp;#160;CIFALPS2 (China-Italy-France Alps seismic survey) temporary experiment, which operated from 2018 to 2020. We use a&amp;#160;2D hybrid waveform simulation method (Zhao et al., 2008) that is reliable and efficient and has a better response to 2D structures compared to conventional 1D waveform inversion methods, in particular&amp;#160;for the dipping&amp;#160;Moho interface of the subduction complex. We compute synthetic receiver functions for a large set of models&amp;#160;compatible with surface geology data, which are then&amp;#160;processed to obtain synthetic CCP depth-migrated stacks. Furthermore, we model the Bouguer gravity data along the same profile&amp;#160;to obtain preferred density distribution. The nature of rocks in the subduction complex&amp;#160;can be inferred&amp;#160;from our synthetical&amp;#160;models.&lt;/p&gt;&lt;p&gt;Compared to&amp;#160;the&amp;#160;results of&amp;#160;the CIFALPS profile in the Central Western Alps&amp;#160;(Zhao et al., 2015), the subduction&amp;#160;along the CIFALPS2 profile has&amp;#160;a shallower&amp;#160;dip angle, which is a significant difference between the two sections. As for velocity and density models, the two sections have a high velocity and high-density wedge in the subduction complex. We argue that the reason for the difference in crustal structures between the two sections may be related to the difference in stress distribution.&lt;/p&gt;&lt;p&gt;Zhao, L., et al. (2008). &quot;A two-dimensional hybrid method for modeling seismic wave propagation in anisotropic media.&quot; Journal of Geophysical Research&amp;#160;&lt;strong&gt;113&lt;/strong&gt;(B12).&lt;/p&gt;&lt;p&gt;Zhao, L., et al. (2015). &quot;First seismic evidence for continental subduction beneath the Western Alps.&quot; Geology&amp;#160;&lt;strong&gt;43&lt;/strong&gt;(9): 815-818.&lt;/p&gt;