Yes, they are.
"Por lo tanto" is a bit more formal, I think
- Tembló anoche; por eso hoy no hay clases.
There was an earthquake last night, that's why there is no school today.
- Hace mucho calor; así que se me antoja un helado.
It's too hot; so I'm craving ice-cream.
- Ha estado lloviendo mucho; por lo tanto, todo está encharcado.
It has been raining a lot; therefore there are puddles everywhere.
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