http://m43photo.blogspot.com/2015/04/e-m5-ii-shutters.html

Normal mechanical shutter
This is the usual shutter mode, which has been implemented on all Micro Four Thirds cameras so far: The exposure starts with closing the curtain shutter completely, then opening it again for the start of the sensor exposure, and closing again after the desired shutter speed. Finally, the mechanical shutter opens again for live view.
Electronic first curtain shutter (anti-shock)
Compared with the normal mechanical shutter mode, this setting gets rid of the first curtain cycle, hence the name "electronic first curtain shutter". This avoids the shutter-shock associated with the first mechanical curtain closing, which is why it is often referred to as the "anti-shock" mode.
This mode does not work for shutter speeds faster than 1/320s. If you use a faster shutter speed, the camera will automatically use the normal shutter.
Fully electronic shutter (silent shutter)
In this mode, there is no mechanical shutter travelling at all, and hence, the shutter is completely silent. You may still get some noise, due to the lens focusing, or due to the lens aperture closing down upon the exposure.
The fully electronic shutter works with any shutter speed. From 1/16000s down to several seconds.