The Moho discontinuity plays an important role in crustal growth and evolution. In this study, we delineate the Moho geometry in southern California by jointly using local Moho-reflected waves PmP and teleseismic Moho-converted waves Ps. To well constrain the Moho geometry, we have developed a two-stage process to pick PmP waves and have created a reliable PmP travel time data set with a total of 10,192 picks. We have also extracted 38,648 high-quality P-wave receiver functions (RFs). The Moho depth is initially estimated via the common conversion point (CCP) stacking of RFs and then refined by inverting the PmP travel time data in a community velocity model (CVM-H, version 15.1.1). The newly built Moho geometry is generally consistent with the California Moho Model version 1.0 (CMM-1.0), that is, a shallow Moho beneath the Salton Trough (23 km), a uniformly shallow Moho beneath the Mojave Desert and the Basin and Range (<29 km), and a sliver of deep Moho under the western Peninsular Ranges, the eastern Transverse Ranges, and the western Sierra Nevada (>34 km). However, our Moho model reveals some new features different from the CMM–1.0, such as a deep Moho (∼34 km) beneath the northern end of the central and western Transverse Ranges, consistent with the observation of deep seismicities due to a thick brittle crust there. We also find a gradual transition from the lower crust to the uppermost mantle beneath the western Peninsular Ranges, leading to the rareness of pickable PmP waves as well as weak Moho-converted signals there.

Adjoint tomography (i.e., full-waveform inversion) has been recently applied to ambient seismic noise and teleseismic P waves separately to unveil fine-scale lithospheric structures beyond the resolving ability of traditional ray-based traveltime tomography. In this study, we propose a joint inversion scheme that alternates between frequency-dependent traveltime inversions of ambient noise surface waves and waveform inversions of teleseismic P waves to take advantage of their complementary sensitivities to the Earth’s structure. We apply our method to ambient noise empirical Green’s functions from 60 virtual sources, direct P and scattered waves from 11 teleseismic events recorded by a dense linear array (～ 7 km station spacing) and other regional stations (～ 40 km average station spacing) in central California. To evaluate the performance of the method, we compare tomographic results from ambient noise adjoint tomography, full-waveform inversion of teleseismic P waves, and the joint inversion of the two data sets. Both applications to practical field data sets and synthetic checkerboard tests demonstrate the advantage of the joint inversion over individual inversions as it combines the complementary sensitivities of the two independent data sets towards a more unified model. The 3D model from our joint inversion not only shows major features of velocity anomalies and discontinuities in agreement with previous studies. but also reveals small-scale heterogeneities which provide new constraints on the geometry of the Isabella Anomaly and mantle dynamic processes in central California. The proposed joint inversion scheme can be applied to other regions with similar array deployments for high-resolution lithospheric imaging.