Notes on reading MQS catalog data files.

The files exactly match the intended namespace design for QuakeML with Mars
extensions.

The files events_extended_multiorigin_*.cxml conform to the published 
QuakeML 1.2 standard and use the namespaces as stated in the standard 
definition. They are compatible with the Python ObsPy catalog module.

The files events_mars_extended_multiorigin_*.cxml contain QuakeML with non-
standard extensions for Mars. These do not conform any longer to the 
QuakeML 1.2 standard. They are designed according to an extended, unpublished 
XML schema with Mars extensions. Please see the MQS schema collection for the 
updated XML Schema files. The catalogue XML file validates against the master 
schema file QuakeML- Mars-1.0.xsd.

Unfortunately, Python ObsPy only understands "official" QuakeML 1.2 documents
because of its strict namespace check. This will generate an error when trying
to read events_mars_extended_multiorigin_*.cxml files. The namespace check is 
not the only difficulty. Much of the relevant Mars extension content lives in
elements that are not seen by ObsPy.

In order to access the full content of the QuakeML with Mars extensions, a 
more low-level XML library like Python lxml should be used.