Avraham's Aliyah


Two Moves?

 The opening of Bereshit 12 speaks of Avraham's migration to Canaan: 

(א) וַיֹּאמֶר י"י אֶל אַבְרָם לֶךְ לְךָ מֵאַרְצְךָ וּמִמּוֹלַדְתְּךָ וּמִבֵּית אָבִיךָ אֶל הָאָרֶץ אֲשֶׁר אַרְאֶךָּ. 
(ד-ה) וַיֵּלֶךְ אַבְרָם כַּאֲשֶׁר דִּבֶּר אֵלָיו י"י וַיֵּלֶךְ אִתּוֹ לוֹט וְאַבְרָם בֶּן חָמֵשׁ שָׁנִים וְשִׁבְעִים שָׁנָה בְּצֵאתוֹ מֵחָרָן... וַיֵּצְאוּ לָלֶכֶת אַרְצָה כְּנַעַן וַיָּבֹאוּ אַרְצָה כְּנָעַן.

From these verses, it sounds as if the move was prompted by a Divine command which instructed Avraham to specifically leave his father's household behind and head to Canaan.  Yet, the end of the previous chapter suggests that the migration of Chapter 12 was only the second stage of a process begun much earlier by Terach:

וַיִּקַּח תֶּרַח אֶת אַבְרָם בְּנוֹ וְאֶת לוֹט בֶּן הָרָן בֶּן בְּנוֹ וְאֵת שָׂרַי כַּלָּתוֹ אֵשֶׁת אַבְרָם בְּנוֹ וַיֵּצְאוּ אִתָּם מֵאוּר כַּשְׂדִּים לָלֶכֶת אַרְצָה כְּנַעַן וַיָּבֹאוּ עַד חָרָן וַיֵּשְׁבוּ שָׁם.  

According to this verse, Avraham's father, Terach, appears to have initiated a move to  Canaan on his own.  What motivated him to uproot his family and head specifically there?  Were his incentives personal, or was his decision connected to the Divine directive recorded only later?

"מֵאַרְצְךָ וּמִמּוֹלַדְתְּךָ"

Hashem's words to Avraham, "לֶךְ לְךָ מֵאַרְצְךָ וּמִמּוֹלַדְתְּךָ" appear to be an instruction to leave his land and birthplace behind.  However, the language of this command is troubling, as Avraham had already left his homeland of Ur Kasdim in the previous chapter.  Is this verse referring to an event which had previously occurred and told here out of chronological order?  Or, alternatively, could Avraham's birthplace be in a location other than Ur Kasdim?

Two other texts bear on the question of Avraham's birthplace, and they too make one wonder about its location: