push work to observers

I have a listener, which receives work in the form of IPayload. The listener should push this work to observers who actually do the work. This is my first crude attempt to achieve this:

public interface IObserver
{
    void DoWork(IPayload payload);
}

public interface IObservable
{
    void RegisterObserver(IObserver observer);
    void RemoveObserver(IObserver observer);
    void NotifyObservers(IPayload payload);
}

public class Observer : IObserver
{
    public void DoWork(IPayload payload)
    {
        // do some heavy lifting
    }
}

public class Listener : IObservable
{
    private readonly List<IObserver> _observers = new List<IObserver>();

    public void PushIncomingPayLoad(IPayload payload)
    {
        NotifyObservers(payload);
    }

    public void RegisterObserver(IObserver observer)
    {
        _observers.Add(observer);
    }

    public void RemoveObserver(IObserver observer)
    {
        _observers.Remove(observer);
    }

    public void NotifyObservers(IPayload payload)
    {
        Parallel.ForEach(_observers, observer =>
        {
        observer.DoWork(payload);
        });
    }
}

Is this a valid approach that follows the observer/observable pattern (i.e. pub sub?)? My understanding is that the NotifyObservers also spins up a threat for each payload. Is this correct? Any improvement suggestions very much welcome.