Full Width Banner Image on Posts page. https://sridharkatakam.com/how-to-add-a-full-width-image-below-header-on-blog-page-in-genesis/

functions.php

add_action( 'genesis_after_header', 'sk_blog_banner' );
/**
 * Full Width Banner Image on Posts page
 *
 * @author Sridhar Katakam
 * @link   http://sridharkatakam.com/
 */
function sk_blog_banner() {
	if ( ! is_home() ) {
		return;
	} ?>

	<div class="blog-banner">
		<img src="http://placehold.it/1600x222&amp;text=Banner" alt="Banner" />
	</div>

	<?php
}

style.css

/* Full Width Banner Image on Posts page
--------------------------------------------- */

.blog-banner {
	text-align: center;
}

.blog-banner img {
	width: 100%;
	vertical-align: top;
}