What is the difference between zu and auf when going to an event?

Question

According to my notes, you'd use zu when you're going to an event. For example:

Wir gehen zu einer Party. – "We're going to a party."
Ich gehe zu einer Hochzeit. – "I'm going to a wedding."

But the DWDS has many examples where auf is used instead:

Wir gehen auf eine Party. – "We're going to a party."
Ich gehe auf eine Hochzeit. – "I'm going to a wedding."

In fact there is one case where both versions are given for the same line:

Ich gehe heute zu/auf eine(r) Hochzeit. (From "Shameless" Three Boys, 2011)

1. What is the difference, if any, in meaning between the two versions? I gather it depends on the verb, for example with ''fahren'' you'd always use ''zu''. But that makes sense since you might be driving to the party without actually taking part; maybe you're giving someone a ride. But ''kommen'' seems to favor ''auf''.
2. I'm not familiar with this meaning of auf, so is this part of a larger pattern or is it just random? I'm thinking it's covered under DWDS definition I.2.d): "bezeichnet die Teilnahme an etw." This would imply that using auf implies a degree of participation and engagement which is missing from zu. Is that correct?

Related: What is the difference between "Zu" and "Auf" in these sentences?

Answer 1

We have some overlapping issue here:

For locations there is a difference between zum and in: Ich gehe zum Bahnhof does not imply you enter the building, similarly ich gehe zur Schule may just indicate a pupil and does not imply, that the the speaker is there or on her/his way towards school.

All of your examples seem to fall under the DWDS: auf meaning I/1/c, participation at some event, since you probably want to interact with other guests.

While this is also covered by DWDS: zu meaning I/1/b specifies direction with the intent to participate, I notice a certain emphasis on the location aspect in the definition.

I have to mention the counter-example: Ich gehe zum Frühschoppen. It is pretty obvious, that one wants to enter the pub and drink as well as talk to others in whatever ratio.

I observe, that in classical music one would more likely use ich gehe in ein/zu einem Konzert (or in eine/zu einer Opernaufführung) and there is not much interaction typically, you take your seat, listen and hopefully enjoy and applaud afterwards. For pop and rock bands auf ein Konzert gehen is more frequently used, and I wonder, if that is due to the event character, as dancing, singing along, clapping the rhythm and waving your lighter?

My summary: zu / auf may not be entirely exchangeable, but the difference is difficult to decide and dependent on context.

Answer 2

If one says Ich gehe auf eine Party this means that s/he will not only go to a party but also attend it. One would usually not say this if s/he goes to a party to e.g. pick someone up or just glance at it and go home.

On the other hand, Ich gehe zur Party can be used if someone goes to a party, but without staying there for a while.

In most cases, the sentences will have the same meaning. But there are cases when the meaning can differ, as explained above.