Femtosecond laser processing of semiconductor wafers is driven by applications in the electronics and photonics industry. X-ray free-electron lasers are powerful probes for revealing the ultrafast dynamics of the induced changes. We present a novel technique that provides time and depth resolved snapshots of the strain field upon laser excitation of bulk crystalline Si. At fluences below the melting threshold, coherent shear waves were found to propagate from the laser-excited surface into the bulk. Simulations support a propagation speed of 5.8km/s, slower than the longitudinal speed of sound, 8.4km/s.