add_filter('relevanssi_modify_wp_query', 'mrb_tax_query');
function mrb_tax_query($query) {
    $tax_query = array();
    if (!empty($query->query_vars['asset_class'])) {
        $tax_query[] = array(
            'taxonomy' => 'asset-class',
            'field' => 'slug',
            'terms' => $query->query_vars['asset_class'],
			'operator' => 'IN'
        );
    }
    if (!empty($query->query_vars['region'])) {
        $tax_query[] = array(
            'taxonomy' => 'region',
            'field' => 'slug',
            'terms' => $query->query_vars['region'],
			'operator' => 'IN'
        );
    }
    if (!empty($query->query_vars['economy'])) {
        $tax_query[] = array(
            'taxonomy' => 'economy',
            'field' => 'slug',
            'terms' => $query->query_vars['economy'],
			'operator' => 'IN'
        );
    }
    if (!empty($query->query_vars['report_type'])) {
        $tax_query[] = array(
            'taxonomy' => 'report-type',
            'field' => 'slug',
            'terms' => $query->query_vars['report_type'],
			'operator' => 'IN'
        );
    }

    if (!empty($tax_query)) {
        $tax_query['relation'] = 'AND'; // you can also use 'OR' here
        $query->set('tax_query', $tax_query);
		$query->set('orderby', 'date');
        $query->set('order', 'DESC');
    }
    return $query;

}