Shares of Sempra Energy rocketed 15% toward a six-month high in active trade Monday, after activist investors Elliott Management and Bluescape Resources revealed a “value creation” strategy that could result in a further 19%-to-35% rally from current levels. Volume ballooned to 9.2 million shares, which was already more than 4-times the full-day average. The investors, which together own a $1.3 billion, or 4.9% stake in Sempra, outlined “ideas and proposals” that if executed, could create $11 billion to $16 billion in value and lift the share price to the $139-to-$158 range. “Despite the attractive characteristics of its businesses, Sempra shares are deeply undervalued by the market,” the investors said in a letter to Sempra. “In our view, this persistent and substantial undervaluation stems from a focus on sheer size that has permeated management and board thinking.” Sempra responded to Elliott and Bluescape’s proposal, by saying it was “committed to an open dialogue with all shareholders,” and that it will review the letter and respond “in due course.” With Monday’s rally, the gas and electric company’s stock has now gained 1.7% over the past 12 months, while the S&P 500 has climbed 14.7%.